Copy in the input structs from libwayland-server

These have been removed in Wayland itself in order to simplify the
server API. The idea is eventually to combine them directly into
ClaylandSeat and friends.

http://cgit.freedesktop.org/wayland/wayland/commit/?id=e920572e5cc1
Rename the symbols for input copied from wayland to cwl_*

That way the code can be used with Wayland 1.1 or master.
Remove the WL_EXPORT attributes