A new GlobalShortcutsManager is introduced which is responsible for
holding the registered shortcuts and triggering the matching action.
The InputRedirection checks with the GlobalShortcutManager whether a key
press event triggers a global shortcut and stops processing the event in
that case.
At the moment the GlobalShortcutsManager only supports the very basics
for KWin internal usage. External applications can not yet make usage of
the global shortcut system inside KWin.
