The _closest() method already defined a way to do what _matches() was
trying to accomplish.  This pulls the functionality out of _closest() so
that it can be reused outside of _closest() but refactors _closest() to
use this new _matches() method.

For instance, say you are sorting tbody's within a table element.  There
can also exist tfoot and thead within the table element.  The _index()
function assumes that the list of elements within the parent is
homogenus (ie: just li's below an ol/ul).  This isnt the case when
sorting tbody under table.  This is edge case until you want to group
tr's under a table and sort on those groupings.

And so on: #558, #547, #542, #537, #532, #516, #500, #489, #489, #447, #475, #459, ##422, #411, #356

when nesting Sortable's, we're not interested in this error:
"HierarchyRequestError: Failed to execute 'appendChild' on 'Node': The new child element contains the parent."

As done in the other place where `dataTransfer` is used.
This is to support fake html5 drag and drop events, where `dataTransfer` is not accessible. Use case: Selenium testing with ePages-de/chromedriver-html5-dragdrop

#356 Fixing issue where dropping an item on the right end of a horizontally layed out drop zone does not add the item

fix http://jsbin.com/cuduyo/edit?html,css,output

compatible with 
flex-direction: row
flex-direction: row-reverse
https://developer.mozilla.org/fr/docs/Web/CSS/flex-direction

_emulateDragOver optimized to reduce the interval tics. 
That provides a fluidity similar to the native drag and drop mode.

see #422

drag/drop handlers should be disabled in fallback mode to avoid unwanted behaviors

removed the default behaviour to append the cloned Element to the body.
now the cloned Element gets added in the same parent, with the addition
of the class defined in options.fallbackClass.
added the possibility to change the fallback class.
added the possibility to decide wheter the fallback should be cloned
into the same parent or to the document's body.