[PATCH 1/2] Convert wl_input_device to wl_seat et al

[Daniel Stone]

Hi,
The following two patches (one each for Wayland and Weston) convert
wl_input_device to a mix of a parent wl_seat interface, as well as
subinterfaces for each of the pointer, keyboard and touch classes.

Each wl_seat may have zero or one wl_{pointer,keyboard,touch} classes,
which are announced dynamically and then bound to by clients, much
like the wl_data_device arrangement.

I've also ported toytoolkit and as you can see, the changes to clients
are fairly trivial - most of the changes are just straight renames,
e.g. weston_input_device -> weston_seat.  Should be pretty
straightforward for most clients.

Cheers,
Daniel