Use DBus activation for applications that are dbus activatable

Use dbus activation as per freedesktop desktop entry spec. https://specifications.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.html#dbus Applications that want to use it need to have DBusActivatable=true in their desktop file, have a dbus-activatable service with the same name as their desktop file and implement the org.freedesktop.Application interface at the object path that results when every '.' in the name of the service is replaced by '/'. KDBusService automatically takes care of registering the name and object that implements the interface. The application just needs to connect to the activate(Action)Requested signals of KDBusService.