jack: add plugin preferences

Up to now, the jack output plugin simply connected to all available ports. However, this is not helpful with audio interfaces that have a high number of ports as you then first have to disconnect all undesired connections before using.

With this patch I've added a simply configuration option exposing the different automatic methods jack offers (ALL, OUTPUT, NONE) the latter of which lets me use one of the available patchbay programs to manage this.