OBS Multiplatform 0.8.0

Changes:
* Added support for multiple audio tracks, enabling the user to stream and record with different mixes (assign/remove sources from tracks via the advanced audio properties)
* Added an 'advanced' output mode in output settings ('Mode' dropdown at the top of output settings)
* Placed a settings-like icon above the mixer to access the advanced audio properties (and make it more visible)
* Fixed the 'streaming' section of settings so that OK/Apply/Cancel work properly
* Added OK/Cancel options to the source properties window
* The program will now display a confirmation message box if exiting while streaming/recording is active

Advanced output mode features:
* Allow the use a different encoder for recording than for streaming (or the same if desired)
* Allow the use of encoders other than x264 if they're available
* Allow streaming and recording at different resolutions
* Allow streaming and recording with different audio tracks
* Allow the ability to optionally use a custom FFmpeg output instead of recording with h264/AAC
