Things not yet implemented in Weston, but used by Maliit Keyboard:
1. IM initiated hiding notifications.
2. Action invoking. By action we mean "copy", "paste" and such. For
   completness we could also pass a key sequences like Ctrl+c for
   copying or Ctrl+v for pasting.
3. Make putting a cursor before commited text possible. For now Weston
   takes an unsigned int which is relative to the beginning of
   commited text.
