Pull UI validation and its helpers to their own class. This class will
be used to validate forms and perform UI-action checks such as
checking stream keys aren't empty and in this diff now holds the logic
to ensure there is a source before the person starts a stream.

Adds an option to the right click menu in the scenes widget to switch
modes. When in regular list mode, it'll let you select grid mode, and in
grid mode, it'll let you select list mode. Grid mode changes the scenes
widget to have a grid of buttons for scenes rather than a list, much
like XSplit.

Most of the top streaming services now have a link in the stream key
label. Upgrading this button to a button clarifies the assistance
for the important step of setting up a stream.

Creates a new type of button for URL opening simply which also
automatically updates the tootip to the current URL.

Includes addition of Twitter/Periscope URL to make this feature more
complete.

_obspython.so currently links directly against python as @rpath/Python
and has 3 common python install paths set as rpaths so it would only
work if a user had python installed at one of those hardcoded paths.

Don't link _obspython against python at all but instead link it with
"-undefined dynamic_lookup" so when it is imported by python all it's
undefined python symbols get resolved at runtime against the user
supplied python instance loaded into the process earlier.

The rpaths aren't needed anymore this way.

Shuts down the actual browsers internally when the browser docks are
hidden by user.

Refactors all cases where a window class was created to show a browser
dock in to one class: BrowserDock.  Removes some unnecessary code
duplication.

This change adds the ability to box select by clicking and dragging from
an empty part of the preview.

Shift + Drag add any items in the box to the selection. Alt + Drag will
remove items in the box from the selection. Ctrl + Drag inverts the
selected state for items in the box.

Allows the ability for users to add custom browser widget docks that
they can use for their third party services if they feel the need,
mostly as a convenience tool so they don't have to open extra browsers
alongside the program.

Adds support for pausing recordings.  When settings are eligible for
recordings, a pause button will appear next to the recording button.  If
the settings are not eligible, it will warn the user in the output
settings that they cannot pause recordings if those settings are used.

The workarounds were made because of conflicts with running multiple UI
threads at once on macOS, which macOS can't do very well, and would be
susceptible to crashes.  This would cause crashes not only on startup
but seemingly at random when using the browser source on macOS.  The
original "fix" was a hack to try to minimize UI code and browser UI code
from executing at the same time.  The macOS initial scene loading was
deferred until all Qt-related and main window initialization was
completed.  Although this worked to some extent to prevent conflicts, it
made it so that there was an initial period on startup where the entire
UI seemed "blank" for users, and it was still possible for the main UI
thread and the browser UI thread to clash, causing crashes seemingly at
random for users.

The external message pump method of CEF is the solution to the problem,
which is the method which allows the main UI thread to share events with
CEF.  To do this, all CEF operations need to be performed in the UI
thread (Qt's main thread), and CefDoMessageLoopWork() needs to be called
when CefApp::OnScheduleMessagePumpWork callback is triggered.  A number
of other issues had to be solved as well, such as CefBrowser references
getting "stuck" in the Qt event queue.

With this, macOS no longer needs to do the "deferred load" hack, and
browsers are now much more stable and no longer as susceptible to
seemingly random crashes, improving overall program stability when
browsers are used.

This changes all of the icons from png to svg. With svgs, scaling is
unlimited. With the svgs, the issue of the @ symbols with the Windows
updater is no longer an issue.

I changed the colors of the icons to a light gray (#d2d2d2), in the
dark themes, because I thought they looked better with this color.

The mute, unmute, plus, minus, up, down and expand icons are from the
Feather Icons set. https://feathericons.com/

The visibility icon is from the Octicons set. https://octicons.github.com/

The locked and unlocked icons are from the Open Iconic set.
https://github.com/iconic/open-iconic

Changes comboBox-* and spinBox-* files to lowercase to be more
consistent with the rest of the files in the UI directory.

Ignore wheelEvent using subclass
slider,spinbox,combobox with eventhandlers:
wheelEvent - ignore if widget is not focused,
leaveEvent - clear focus when mouse leaves event.

Use these new subclass widgets in properties
to ignore wheelEvent when scrolling.

Fixes the `obs.rc` file appearing in the UI source tree and moves it
into the out-of-tree build directories provided by CMake. Projects
requiring this can use it by adding `${obs-studio_BINARY_DIR}/obs.rc`
to their source list.

Closes obsproject/obs-studio#1768

Users don't realize that dockable windows can be closed (hidden) and can
be shown again via the View menu.  This adds an explicit warning when
the user first closes a dockable window for their first time.  In future
versions, this should be changed to a dialog box with a "Do not show
again" checkbox.

You could also say..  obs-fuscation.

Allows the ability to authenticate to a specific service.  Typically via
OAuth.

Allows the ability to switch cookies between profiles.  Allows the
ability to, for example, switch streaming service accounts between
profiles for proper access to the pages displayed by the browser panels
(such as chat windows).

Makes it so that services can have custom handling on a per-service
basis.  The bottom part of the service pane is now a stacked widget
which can now be customized for different types of services
(particularly OAuth services).

Currently, browser panel is only supported on windows.  So rather than
have to check for _WIN32 in the code everywhere, just move the WIN32
check to cmake, that way we don't have to have _WIN32 checks in the code
everywhere the browser panel code is used, and do not have to remove a
whole bunch of unnecessary _WIN32 #ifdefs for other operating systems
when browser panel support is added for them.

Use /LARGEADDRESSAWARE linker option when compiling 32bit executables on
Windows.

Closes obsproject/obs-studio#1546

The UI currently is dependent on browser source files being present,
when in actuality the files may not have been fetched (i.e. not fetching
submodules).  This fixes that by using a macro to detect whether it's
available or not.

Closes obsproject/obs-studio#1490

This commit adds the ability to select a background color for a
scene-item, whether it's a custom color or one of eight presets.

As this is an initial implementation, it lacks theme customizability,
and it also lacks the ability for the user to set their own preset
colors, so only the hard-coded 8 are available.

Allows the ability to show a web page via CEF to the users on startup to
present and announce new features.