core, bridge: new signal actionNew to launch an action from the backend (e.g. display a dialog message): - SAT.actionNew is a shortcut to call bridge.actionNew with a generated id. The id may be used in the future to ignore an action (e.g.: an action is sent to all frontends to accept a file, one of the frontend did manage the dialog, the other ones can then ignore this dialog), but is not used for now.