This commit adds a combo box for selecting ports.
Overall this implementation could have taken two paths:
* Implement port selection as combo box.
* Implement port selection as a button.
I went for the first option as is done in selecting card profiles over the
second method used for selecting devices for streams. This seems more like
how a config option should be presented as opposed to a runtime type thing.
I reworked the way this was done so we can easily re-enable this as I think it's clearer when it's inactive
(the difference between toggled and not toggled is pretty minor).
With this abstraction we could reset the tooltip etc. too.
Lennart Poettering