evdev: fix X11 to evdev keycode translation

Hardware keycodes in Clutter events are x11 keycodes, which are
the same as evdev + 8, but we need to reverse the translation when
explicitly asked for an evdev keycode.

https://bugzilla.gnome.org/show_bug.cgi?id=705710
evdev: fix xkb_state handling

We must pass X11 keycodes, not evdev ones, to libxkbcommon,
otherwise the modifier state is wrong.

https://bugzilla.gnome.org/show_bug.cgi?id=705710
evdev: remove dead code

ClutterDeviceManager uses g_object_new directly, to pass the
necessary properties down.

https://bugzilla.gnome.org/show_bug.cgi?id=705710
evdev: add master / slave device handling

All evdev devices are slave devices, which means that xkb state
and pointer position must be shared by emulating a core keyboard
and a core pointer. Also, we must make sure to add all modifier
state (keyboard and button) to our events.

https://bugzilla.gnome.org/show_bug.cgi?id=705710
evdev: allow hooking directly into libxkbcommon

A wayland compositor needs to have more keyboard state than
ClutterModifierState exposes, so it makes sense for it to use
xkb_state directly. Also, it makes sense for it to provide
it's own keymap, to ensure a consistent view between the compositor
and the wayland clients.

https://bugzilla.gnome.org/show_bug.cgi?id=705710
evdev: don't update xkb state for autorepeated keys

xkb_state_update_key() needs to be called only on state transitions,
otherwise the state tracking gets confused and locks certain modifiers
forever.

https://bugzilla.gnome.org/show_bug.cgi?id=705710
evdev: implement wheel events

Mouse wheel events come as EV_REL/REL_WHEEL, and we can convert
them to clutter events on the assumption that scrolling with
the wheel is always vertical.

https://bugzilla.gnome.org/show_bug.cgi?id=705710