Lyude Paul authored Jan 18, 2015 and Carlos Garnacho committed Apr 06, 2016

Only the management of tablets and tools is added so far. No tablet events
are yet interpreted.

As it's been the tradition in GTK+, erasers are split into their own device,
whereas the rest of the tools are meant to be routed through the
GDK_SOURCE_PEN device. Both pen/eraser devices are slaves to a master
pointer device, separate to wl_pointer's. This is so each tablet can
maintain its own cursor/positioning accounting.

Signed-off-by: Stephen Chandler Paul <thatslyude@gmail.com>