update form controls to newest bootstrap

pages/_includes/forms/form-elements-1.html

-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Static</label>
    <div class="form-control-plaintext">Username</div>
 </div>
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Text</label>
    <input type="text" class="form-control" name="example-text-input" placeholder="Text..">
 </div>
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Disabled</label>
    <input type="text" class="form-control" name="example-disabled-input" placeholder="Disabled.."
           value="Well, she turned me into a newt." disabled>
 </div>
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Readonly</label>
    <input type="text" class="form-control" name="example-disabled-input" placeholder="Disabled.."
           value="Well, how'd you become king, then?" readonly>
 </div>
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Textarea <span class="float-right text-muted-light">56/100</span></label>
    <textarea class="form-control" name="example-textarea-input" rows="6" placeholder="Content..">Oh! Come and see the violence inherent in the system! Help, help, I'm being repressed! We shall say 'Ni' again to you, if you do not appease us. I'm not a witch. I'm not a witch. Camelot!</textarea>
 </div>
@@ -25,7 +25,7 @@
 
 {% include parts/input-color.html %}
 
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Input group</label>
    <div class="input-group">
       <input type="text" class="form-control" placeholder="Search for&hellip;">
@@ -34,7 +34,7 @@
 						</span>
    </div>
 </div>
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Input group buttons</label>
    <div class="input-group">
       <input type="text" class="form-control">
@@ -60,7 +60,7 @@
 
 {% include parts/input-icon.html %}
 
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Separated inputs</label>
    <div class="row row-xs">
       <div class="col">
@@ -71,7 +71,7 @@
 						</span>
    </div>
 </div>
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">ZIP Code</label>
    <div class="row row-sm">
       <div class="col">

pages/_includes/forms/form-elements-2.html

-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Password</label>
    <input type="password" class="form-control" name="example-password-input" placeholder="Password..">
 </div>
 
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Valid State</label>
    <input type="text" class="form-control is-valid" name="example-text-input-valid"
           placeholder="Valid State..">
@@ -11,7 +11,7 @@
    <input type="text" class="form-control mt-3 state-valid" value="Valid state">
 </div>
 
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Invalid State</label>
    <input type="text" class="form-control is-invalid" name="example-text-input-invalid"
           placeholder="Invalid State..">
@@ -20,42 +20,42 @@
    <input type="text" class="form-control mt-3 state-invalid" value="Invalid state">
 </div>
 
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Country</label>
    <select class="form-control custom-select">
       <option value="">Germany</option>
    </select>
 </div>
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Ratios</label>
    <input type="range" class="custom-range" step="5" min="0" max="50">
 </div>
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Size</label>
    {% include ui/input-selectgroup.html values="S,M,L,XL,XXL" type="radio" name="size" %}
 </div>
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Shipping methods</label>
    {% include ui/input-selectgroup.html values="Unregistered,Priority Mail,Express Mail" class="selectgroup-vertical" type="radio" name="shipping-method" %}
 </div>
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Icons input</label>
    {% include ui/input-selectgroup.html values="i:smartphone,i:tablet,i:monitor,i:x" class="w-100" type="radio" name="device" %}
 </div>
 
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Icon input</label>
    {% include ui/input-selectgroup.html values="i:sun,i:moon,i:cloud-rain,i:cloud,Other" class="selectgroup-pills" %}
 </div>
 
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Your skills</label>
    {% include ui/input-selectgroup.html values="HTML,CSS,PHP,JavaScript" class="selectgroup-pills" %}
 </div>
 
 {% include parts/input-toggle.html %}
 
-<div class="form-group">
+<div class="mb-2">
    <div class="form-label">Toggle switch single</div>
    <label class="custom-control custom-switch">
       <input type="checkbox" class="custom-control-input">
@@ -63,7 +63,7 @@
    </label>
 </div>
 
-<div class="form-group">
+<div class="mb-2">
    <div class="form-label">Radios</div>
    <div class="custom-controls-stacked">
       <label class="custom-control custom-radio">

pages/_includes/forms/form-elements-3.html

-<div class="form-group">
+<div class="mb-2">
    <div class="form-label">Inline Radios</div>
    <div class="custom-controls-stacked">
       <label class="custom-control custom-radio custom-control-inline">
@@ -18,7 +18,7 @@
       </label>
    </div>
 </div>
-<div class="form-group">
+<div class="mb-2">
    <div class="form-label">Checkboxes</div>
    <div class="custom-controls-stacked">
       <label class="custom-control custom-checkbox">
@@ -43,7 +43,7 @@
       </label>
    </div>
 </div>
-<div class="form-group">
+<div class="mb-2">
    <div class="form-label">Inline Checkboxes</div>
    <div>
       <label class="custom-control custom-checkbox custom-control-inline">
@@ -63,7 +63,7 @@
       </label>
    </div>
 </div>
-<div class="form-group">
+<div class="mb-2">
    <div class="form-label">Bootstrap's Custom File Input</div>
    <div class="custom-file">
       <input type="file" class="custom-file-input" name="example-file-input-custom">
@@ -71,7 +71,7 @@
    </div>
 </div>
 
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Date of birth</label>
    <div class="row row-xs">
       <div class="col-5">
@@ -109,27 +109,27 @@
 </div>
 
 
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Username</label>
    {% include ui/input-group.html prepend="@" placeholder="username" %}
 </div>
 
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Subdomain</label>
    {% include ui/input-group.html append=".tabler.io" placeholder="subdomain" %}
 </div>
 
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Your vanity URL</label>
    {% include ui/input-group.html prepend="https://example.com/users/" %}
 </div>
 
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Price</label>
    {% include ui/input-group.html prepend="$" append=".00" %}
 </div>
 
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Button input</label>
    <div class="input-group">
       <div class="input-group-prepend">
@@ -149,12 +149,12 @@
    </div>
 </div>
 
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Tags</label>
    <input type="text" class="form-control" id="input-tags" value="aa,bb,cc,dd">
 </div>
 
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Beast</label>
    <select name="beast" id="select-beast" class="form-control custom-select">
       <option value="1">Chuck Testa</option>
@@ -163,7 +163,7 @@
    </select>
 </div>
 
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Users list</label>
    <select name="user" id="select-users" class="form-control custom-select">
       {% for user in site.data.people limit: 10 %}
@@ -174,7 +174,7 @@
    </select>
 </div>
 
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Countries</label>
    <select name="country" id="select-countries" class="form-control custom-select">
       <option value="br" data-data='{"image": "{{ site.base }}/assets/images/flags/br.svg"}'>Brazil</option>

pages/_includes/forms/form-elements-5.html

-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Text mask</label>
    {% include ui/input-mask.html mask="00/00/0000" placeholder="00/00/0000" visible=true %}
 </div>
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Telephone mask</label>
    {% include ui/input-mask.html mask="(00) 0000-0000" placeholder="(00) 0000-0000" visible=true %}
 </div>
 
-<div class="form-group">
+<div class="mb-2">
    <label class="form-label">Autosize textarea</label>
    <textarea class="form-control" data-toggle="autosize" placeholder="Typing something&hellip;"></textarea>
 </div>