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
Identifier list was filled and more and more identifiers got checked via DBus
- identifier set if only one unique identifer is needed
- using set avoids duplicates and fixes the bug
- restart time if registered, no need to check again
