[application] The application termination via DBUS should consider 'OnSu...

...spend' event handlers.

The application DBUS proxy should consider the fact that an
application might be still running even after its "Terminate"
method is called (if termination mode is 'Normal' and the app
contains 'OnSuspend' handlers) so it still should listen to
'owner' changes. Besides, the DBUS client should be able to
enforce termination - might be needed for example if 'OnSuspend'
event takes too long time and the User wants to stop the app
immediately.
This patch exports a new "ForceTerminate" DBUS method from
application proxy object and modifies its termination logic
accordingly to the requirements described above.