evdev: Add evdev specific event filter function

This function can be used to intercept or translate events
that are unmanaged by clutter itself.

https://bugzilla.gnome.org/show_bug.cgi?id=728967
evdev: Add function to get the libinput_device from a ClutterInputDevice

This may be useful for deeper libinput integration that's not in the scope
of Clutter.

https://bugzilla.gnome.org/show_bug.cgi?id=728967