Tiberian Sun .vqa support

Ref : #3363,#3226

This is very much WIP so it is even messier than usual.

Progress so far is:
Most videos load and play without crashing, but the audio is somewhere between stretched out and complete noise. The video only displays some shapes correctly (the spinning EVA logo is the easiest to see), but all colors are wrong and the image is flipped https://imgur.com/NG1yvFc.jpg ([Original video](https://www.youtube.com/watch?v=xuNN9ACgTFg)).
So still left to do is:
- [x] Fix image orientation
- [x] Fix colors
- [x] Fix audio playback
- [x] Performance improvements (Some videos have ~1 sec stutters) 
- [x] Fix crashes with certain videos (I'm not sure if diskdest.vqa is a proper video anyway)

The changes to gitignore and to the asset browser are just for testing so they can be removed once this is complete.

Also credit for reverse engineering goes to [olafvdspek's XCC Mixer](https://code.google.com/p/xcc/).

OpenRA code style is to have a newline between the closing brace of a block and the next line.  Stylecop will pick up this class of issues.