libobs: Add surround sound audio support

(This commit also modifies the following modules: UI,
deps/media-playback, coreaudio-encoder, decklink, linux-alsa,
linux-pulseaudio, mac-capture, obs-ffmpeg, obs-filters, obs-libfdk,
obs-outputs, win-dshow, and win-wasapi)

Adds surround sound audio support to the core, core plugins, and user
interface.

Compatible streaming services: Twitch, FB 360 live
Compatible protocols: rtmp / mpeg-ts tcp udp
Compatible file formats: mkv mp4 ts  (others untested)
Compatible codecs: ffmpeg aac, fdk_aac, CoreAudio aac,
		   opus, vorbis, pcm (others untested).
Tested streaming servers: wowza, nginx
	 HLS, mpeg-dash : surround passthrough
Html5 players tested with live surround:
	 videojs, mediaelement, viblast (hls+dash), hls.js
Decklink: on win32, swap channels order for 5.1 7.1
         (due to different channel mapping on wav, mpeg, ffmpeg)
Audio filters: surround working.
Monitoring: surround working (win macOs linux (pulse-audio)).
VST:	 stereo plugins keep in general only the first two channels.
	 surround plugins should work (e.g. mcfx does).
OS: win, macOs, linux (alsa, pulse-audio).
Misc: larger audio bitrates unlocked to accommodate more channels
NB: mf-aac only supports mono and stereo + 5.1 on win 10
         (not implemented due to lack of usefulness)

Closes jp9000/obs-studio#968

plugins/decklink/data/locale/en-US.ini

@@ -12,6 +12,13 @@ ColorRange.Full="Full"
 ChannelFormat="Channel"
 ChannelFormat.None="None"
 ChannelFormat.2_0ch="2ch"
+ChannelFormat.2_1ch="2.1"
+ChannelFormat.3_1ch="3.1"
+ChannelFormat.4_0ch="4ch"
+ChannelFormat.4_1ch="4.1ch"
 ChannelFormat.5_1ch="5.1ch"
-ChannelFormat.5_1chBack="5.1ch (Back)"
+ChannelFormat.5_1chBack="5.1ch Back"
 ChannelFormat.7_1ch="7.1ch"
+ChannelFormat.7_1chBack="7.1ch Back"
+ChannelFormat.8_0ch="8.0ch"
+ChannelFormat.16_0ch="16.0ch"