[X11] Added XKB bindings
[X11] Use XKB for layout-independent input

The code will fall back to core X11 if XKB is not available.
[X11] Rebased on develop branch
[X11] Added XIDeviceType enumeration
[X11] Implemented XI2 keyboard input
[X11] Split X11 and XI2 input drivers
[X11] Renamed XI2Mouse

This file now implements both mouse and keyboard input, so its name
has been updated to reflect that.
Merge branch 'xkeyfix' of https://github.com/thefiddler/opentk into develop