TrackIR SDK Support

I really wanted to play KSP using my TrackIR 5 and was mildly disappointed when I found out that KerbTrack couldn't use FreeTrack to hook into anything newer than TrackIR 4 so I decided to add support myself using the official TrackIR SDK.

The additions rely on [UnityTrackIR.dll](https://github.com/byBrick/Unity-TrackIR-Plugin) which acts as a bridge between Unity and TrackIR's SDK. Unfortunately the plugin didn't support 64bit so I [patched it](https://github.com/medsouz/Unity-TrackIR-Plugin-DLL).

I tried to have as little of an impact on the codebase as possible so I created an interface for different tracking SDKs. (currently just FreeTrack and TrackIR but this could be used in the future to add Oculus Rift support)

If you have any questions/comments/things you want me to change feel free to ask!