Use the current Gamepad API

`webkitGetGamepads` is deprecated in recent browser versions. Provide use of the current API if available.
[VERSION] v0.156.0-dev
[FIX] pc.Quat#slerp now handles identical input quaterions correctly
Added CONTRIB file

Fixed some spelling.
Update CONTRIB file with CLA details and tips
Merge pull request #38 from Systemcluster/patch-1

Use the current Gamepad API
[FIX] audiosources with 'activate' false no longer play on startup
[RELEASE] v0.155.1