Refactor the remote hotkeys to avoid round trips

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

src/blackcore/context/contextapplicationempty.h

@@ -135,7 +135,7 @@ namespace BlackCore
             }
 
             //! \copydoc IContextApplication::callHotkeyAction
-            virtual void callHotkeyAction(const QString &action, bool argument, const BlackMisc::CIdentifier &origin) override
+            virtual void callHotkeyActionRemotely(const QString &action, bool argument, const BlackMisc::CIdentifier &origin) override
             {
                 Q_UNUSED(action);
                 Q_UNUSED(argument);