Change FlyingCamera::Render to support camera panning

Render now takes yawOffset and pitchOffset (both defaulted to 0.0), which are applied to the rotation transform used for the cameras.
Add the ability to support button releases

Currently only plumbed to background handlers.  They will propagate a button release event to the subscribing handler.
Add a steerable camera background handler.

Lengthy comment at the top of the file explains configuration options.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	RasterPropMonitor/Core/ButtonHandler.cs
Merge pull request #5 from MOARdV/master

Add JSISteerableCamera