Extracted the input system from the window manager service into
a new input manager service. This will make it easier to
offer new input-related features to applications.
Cleaned up the input manager service JNI layer somewhat to get rid
of all of the unnecessary checks for whether the input manager
had been initialized. Simplified the callback layer as well.
Change-Id: I3175d01307aed1420780d3c093d2694b41edf66e
4532e61584