The previous implementation was hard to follow and maintain. Instead of
doing intentional rounds trips, we use now a two way approach. GUI is
automatically forwarding remote actions by calling "callHotkeyActionRemotely"
through DBus. Core on the other hand, emits a signal "remoteHotkeyAction"
that is processed in a different function in GUI.
On both sides, actions from the same local machine are filtered.
ref T402
The main reason why CInputManager was singleton is the easy access across
the code. That had the negative side effect that time of destruction was
at a very late stage of the shutdown and could not be controlled by us.
My moving it to CApplication, the access is equally easy (using sApp) and
allows to be cleaned up properly during graceful shutdown.
ref T391
