Add support for mouse hover and scroll wheel.

Dispatch ACTION_HOVER_MOVE and ACTION_SCROLL through the View
hierarchy as onGenericTouchEvent.  Pointer events dispatched
this way are delivered to the view under the pointer.  Non-pointer
events continue to be delivered to the focused view.

Added scroll wheel support to AbsListView, ScrollView,
HorizontalScrollView and WebView.  Shift+VSCROLL is translated
to HSCROLL as appropriate.

Added logging of new pointer events in PointerLocationView.

Fixed a problem in EventHub when a USB device is removed that
resulted in a long stream of ENODEV errors being logged until INotify
noticed the device was gone.

Note that the new events are not supported by wallpapers at this time
because the wallpaper engine only delivers touch events.

Make all mouse buttons behave identically.  (Effectively we only
support one button.)

Change-Id: I9ab445ffb63c813fcb07db6693987b02475f3756