Revert "actor: Plug a leak in the implicit transition removal"

This reverts commit 158af1ff594d8984b59dcf90654ed04cd8c53e16.

This commit introduced a regression, so the leak will have to be fixed
in another way.
Avoid a compiler warning

Initialize a pointer variable.
gdk: Disable deprecation warnings

We don't want to break the build because GDK deprecated some symbol.
gdk: Use non-deprecated GdkCursor API

The non-display safe variant has been deprecated in GTK+ 3.15.
image: Do not put large textures in the atlas

Atlasing is fine for smaller textures, but once they get too large its
downsides outweight the benefits. At worst, the larger texture will end
up inside its own atlas, but at worst it will require copying and/or
resizing of an existing atlas.

The cut-off at 512x512 pixels is a bit arbitrary, and we can change it
at any point; it would be nice if we could get the texture limit from
Cogl, and then use a fraction of that size as the cut-off limit. Sadly,
that's not portable, and it's not guaranteed to work either.
evdev: Prefer pointer/touch devices over keyboard devices

In keyboard/mouse wireless combos, it is rather common for the mouse to
claim it contains the multimedia keys, this makes libinput enable both
the pointer and keyboard capabilities on this device, and Clutter thus
to create a keyboard ClutterInputDevice for it.

Ideally clutter devices should be able to reflect their full capabilities,
or maybe account for the fact that certain events can be sent from
seemingly unexpected device types. But this will bring a somewhat better
behavior on such devices.

https://bugzilla.gnome.org/show_bug.cgi?id=740518
evdev: Lookup config to report touchpads as such

Check a touchpad-only setting, and if it returns an expected value there,
the device must be a CLUTTER_DEVICE_TOUCHPAD.

https://bugzilla.gnome.org/show_bug.cgi?id=741350
x11: Resort to device name matching for non-mt touchpads

If a touchpad is not multitouch, or does not report MT axes (eg. through
the libinput driver), resort to name matching before falling back to
CLUTTER_POINTER_DEVICE.

https://bugzilla.gnome.org/show_bug.cgi?id=741350
Bump up the version to 1.21.1
Add 1.22 version macros

The 1.22 cycle did start a while ago.
docs: Add versioned indexes

We have a bunch of versions to cover.
clutter: add Mir windowing/input backend

Added support for Mir, now clutter can natively draw on MirSurfaces.
This depends on latest cogl git.

Run your clutter apps using COGL_BACKEND=mir