Use the new session shortcut feature for kwins "Window Shorcut" feature.

Please have a look at commit 863096 too. I accidently commited a part of this part there.

Please have a look at the todo "Add the window title" and possibly implement it.
That would look much nicer in the global shortcuts kcm.

Btw. There are two shortcuts dialogs in kwin.
I haven't changed the other one (kwinrules) because it look it works better with KKeySequenceWidget doing the message box.