This adds the management code to manage tablet tools lifetimes from
libinput.
It follows the suggestion made in the tablet-unstable-v2.xml to destroy
tablet_tools once all tablets that it got into contact with were removed
from the system. This is implemented via a refcount.

If a tool is *not* unique, it will be destroyed on proximity out. This
is libinput specific and mentioned in libinput docs that tools will not
be found again, so we shouldn't keep a reference to them.
Also they can't be on other tablets as well, because they cannot be
tracked.

The naming in this commit is a bit off (to not break things).
The wlr names stay the same, tablet_tool is the libinput_device with
capaiblity LIBINPUT_DEVICE_CAP_TABLET_TOOL which is more akin to
"tablet" in the tablet-unstable-v2 protocol.
The struct that corresponds to the tablet_tool in tablet-unstable-v2 is
called tablet_tool_tool, a rename should be done at some point in the
future.

screencopy: fix segfault when client supplies invalid buffer

This reverts commit a0afedcd.

Add wlr_surface.opaque_region

Unbreak xvfb

surface: replace wlr_surface_set_role_committed with wlr_surface_role

Otherwise running under Xvfb will not deliver any events. This results
in e.g. weston-info reporting a 0x0 window size (which results in all
sorts of problems).

So far we did not check for any errors

util: add wlr_ prefix to log symbols

fix: handle 32 bit time_t (or smaller)

Rename wl_resources to resource, wl_global to global

Bail from setting gamma on destroyed resource

xdg-output: don't send no-op updates

To begin with, no-op updates are unnecessary, so this patch is an
improvement on its own.

Then, this fixes hotplugging issues with xwayland. xwayland waits
for both wl_output and xdg_output to send a "done" event. However,
it doesn't handle well desynchronized "done" updates: if xdg-output
sends "done" twice, the second one will wait for the next wl_output
"done" event. This is an issue when the first is a no-op and the
second is a real update: the second isn't applied. I've considered
patching xwayland instead, but it seems pretty complicated.

output: make wl_output resources inert

Allow to add additional modes to outputs

This allows to pass custom modes.

This allows to add additional modes to the list of available video modes
using VESA Coordinated Video Timing information.

Closes #1080

surface: redesign state

These can be set to e.g. regions larger than the surface. If the
surface resizes itself, it doesn't need to set again these regions.