initial startup UX

[Be-ing]

I recently tried jack_mixer for the first time and found the UX confusing. My first question upon seeing the lack of JACK ports in Catia was "how do I connect an application to this?". I asked @dsheeler and he informed me that I had to create an input and output before making connections. I suggest changing this so that jack_mixer automatically creates one input and one output by default and let the user add more if they want. I also suggest to make it more obvious how to add mixer channels by adding "+" adjacent to the last input/output in the main window so users don't need to dig into the menu.