This change makes it so OBS will still launch even if a theme is
missing. This change also deprecates the "CurrentTheme" config key, and
is replaced by "CurrentTheme2".

This is because a previous change to make sure OBS fell back to the
System theme in case of a missing theme had been accidentally removed.
Changing the key prevents a new version of OBS setting a theme that
doesn't exist in an older version, which would prevent that version from
launching.

rtmp-services: Add YouStreamer

(This commit also modifies the UI module)

CI: Fix error deleting QT network framework on OSX

CI: Fix mbedtls id in mac deploy script

obs-ffmpeg: Enable VAAPI Rate Control

libobs: Null check hotkey device on macos

CI: Fix framework symlinks when building osx app

rtmp-services: Increase FB max bitrate to 6Mbps

Allows the ability to save replays with a button rather than with the
keyboard if desired.

Closes obsproject/obs-studio#1954

Facebook Live now recommends 6000kbps for most streamers and the auto
capping is clamping users to 4000kpbs. This fixes the new suggested
setting.

Enable choosing CBR, CQP and VBR.

UI: Streaming Settings Validation On Stream Start & User Help

When we use the server error to respond to user's failing to start a
stream it is slow to return an error and unclear to the user what went
wrong. This diff introduces a simple settings check before attempting
to stream and catch and explain specific URL/key issues to the user.

In the case of preset services we check there is a Stream Key before
attempting to start a stream.

In the case of "custom" we only verify there is a URL since for some
services that's all that is required or the user may use user/password
authentication.

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.

UI: Add Grid Mode to Scenes Widget

rtmp-services: Add Konduit.live

Closes obsproject/obs-studio#2224

UI: Allow switch to existing theme to reload

libdshowcapture: Update to latest submodule

This is useful for people modifying the currently selected theme.

UI: Don't modify theme if already set

This includes reselecting the existing selection, and cancelling out of
settings altogether. Takes a long time (7 seconds) in debug builds.

Decklink: Explicit casts for truncation warnings

libobs: Remove C99 hacks for older VC++

Fixes an issue where when trying to connect a Twitch account, and the
Twitch two-factor authentication check fails, the user will still
technically be logged in because the cookies will still be present, thus
when they try to click the "Connect" button again, it will skip the
login part (because they're already technically logged in), and just
give them the two-factor failure message without letting them enter in
their login information again.

In the current user interface code, OBSBasic::AddSceneCollection has a
qname parameter to allow explicitly specifying a name, but that code
path is unused in the UI code itself, and qname is typically empty.  If
qname is not empty, it does not properly generate a file name associated
with that specified scene collection name.  This fixes that issue.