Modify the current StatusbarController API so that it can be used by pure UNO
implementations

(cherry picked from commit 059f35d0)

Conflicts:
	offapi/com/sun/star/frame/StatusbarController.idl
	offapi/com/sun/star/frame/XStatusbarController.idl

Change-Id: I664a104bff35a35d4406d98f96bdf8983b452ebd