Bug 987529 - Part 1: Integrate GeckoTouchDispatcher into vsyncdispatcher

For inputdispatcher, the register is not one-shot. Actully, we call
register only once for each multitouch sequence.
Bug 1043822 - Support SW Vsync Timer

1. Use nanosleep to implement SW Vsync Timer
2. Add soft vsync timer support for PlatformVsyncTimer
3. Add SetPriority() to PlatformVsyncTimer (Default nice value is -2)
4. Add FrameUniformityForceSWVsync pref
Enable SW Timer