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.

Closes jp9000/obs-studio#1127

Allows for projects other than UI to be able to reference these CMake
variables.

Adds a lock checkbox to allow the user to lock a specific scene item.

Closes jp9000/obs-studio#949

Shows performance stats, and streaming/recording stats, and helps warn
the user when they have less-than-optimal values with coloring on the
values (e.g. yellow when getting low on disk space, red when getting
really low)

The auto-configuration wizard is designed to allow first-time or
novice/uneducated users or to set up video and encoding settings in a
very quick and easy way.  It'll automatically perform a bandwidth test,
and/or test the user's video settings to determine the most ideal
settings for streaming and recording (assuming a 1-pc setup).

Just directly includes the ff-util.c/h files in to UI to prevent the
need of compiling libff in full.