User can now select target RHI's for windows under: Edit->Project Preferences->Windows->Targeted RHIs
Split up GetShaderFormats into GetAllPossibleShaderFormats and GetAllTargetedShaderFormats.
D3D11 and D3D10 remain the only two on, by default, for windows.
#ReviewedBy Nick.Penwarden
[CL 2068025 by Terence Burns in Main branch]
Moved functions to check for and select Compressed Audio Info class to the audio device as the audio formats are not accessible in cooked builds (and shouldn't really need to be either).
[CL 2057758 by Matthew Griffin in Main branch]
Added an audio format for Opus, which also required a resampler to make sure that all imported sounds are converted to a compatible sample rate.
Added the speex resampler from the opus tools package to the third party source, including built libraries for windows and mac.
Changed FVorbisAudioInfo so that it inherits from an interface for any kind of compressed audio, which can be used everywhere instead of being wrapped in #WITH_VORBIS.
Added FOpusAudioInfo to decompress Opus data, not sure at this point whether it's only going to be used for streaming audio but works for non-streamed playback.
[CL 2056352 by Matthew Griffin in Main branch]
#proj Engine
#branch UE4
#summary Added GetFormatCapabilities to ITextureFormat interface, TextureCompressorModule attempts to downsample images that are too large.
#add GetFormatCapabilities to ITextureFormat and all affected subclasses.
#change BuildTextureMips now attempts to construct a source that is compatible with the maximum size for a texture compressor.
[CL 2053233 by Allan Bentham in Main branch]
Phase 1
Added platform to the cooked file requests so that the cooker just cooks files for the requested platform.
Reviewed Daniel Wright
[CL 2038767 by Daniel Lamb in Main branch]
