Linux support

[ChristophHaag]

This project almost "just works" on Linux. I've done this:
ChristophHaag@5f6fd48
Adding submodules for the required projects and some other small fixes should be self explanatory.
I threw out the openvr libraries and header, because in my experience, only the actual OpenVR 1.0.6 interface works on Linux.

Some info on how to compile and run this stuff would be good. Like tl;dr:

• Go to zephyr/desktop/app, run npm install, with having electron installed run electron .
• Go to overlay/src, run qmake; make, run overlay/bin/win32/zephyr
• Run the android app and connect to the ip:port the desktop app displays

So, uhm... success I guess:

Only the overlay settings screen is just rendering garbage. Maybe that is because it's not been properly updated for the most recent OpenVR API? After all I had to replace vr::API_OpenGL with vr::TextureType_OpenGL, maybe other stuff needs to be changed too.

[ThomasGaubert]

Looks good! Right now I'm focusing on re-writing nearly everything for v2. Part of this includes cleaning up the (honestly terrible) overlay, updating to the latest OpenVR, and improving documentation.

Seeing how Linux support doesn't look to require too much additional work, I can look into officially supporting it with or soon after the v2 update.

[ThomasGaubert]

Closing this issue as it was already migrated to the new repository.