Require libinput 0.4.0

No functional changes, just adjusting for API changes in libinput:
- libinput_destroy() replaced by libinput_unref()
- log functions now take a libinput context, userdata is gone
- udev seat creation is now libinput_udev_create_context() and
  libinput_udev_assign_seat()

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>