gui: add keyboard support for Ctrl layer and more special keys

- rename NotifyKeyboard to NotifyCharInput
- input: handle arrow keys in NotifyKey with standard KEY_* codes
- fix page handler to return 0 from NotifyKey if key was handled
- fix GUIAction::NotifyKey to not swallow all keys
- change home button code from KEY_HOME to KEY_HOMEPAGE
  (to avoid collision with Home/End, conforms to Android 3.0+)

Change-Id: Ib138afa492df8d0c1975415e8b5334c8778ccc90