Added basic input framework.

Added basic input framework.

Added xw::Seat to wrap wl_seat and WaylandInput to be the central
control object for keyboard and mouse input.

EventListener is a pure virtual class that WaylandInput delegates
to. EventDispatch implements EventListener and forwards input
and focus events on to XBMC.

Let WinEventsWayland manage the wl_seat * from EGLNativeTypeWayland
once it appears