Fix Icon Switching, System Alert Device, Add Priority Overrides per Speaker/Headphone, and Add Fast Switching

[jhenkens]

Bunch of commits - I can break them out if you like some but not all.

1. Add a preferences window that contains the start-at-login setting intitially
2. Fix the icon switching back to how it was in the releases - Headphone/Speaker Icon.
3. Add the ability to assign an input device as a priority device for a given output device. This way you can prefer your webcam microphone, unless you are using your headphones, then prefer the headphone microphone.
4. Add one-click fast switching as an option in the preferences pane. It requires a restart, but makes left click toggle between Headphone and Speakers, and right click bring up the dialog
5. Add, with a preference, the System Default Output to be switched alongside the Default Output. This wasn't being switched before, and it seems when interacting via these APIs, OSX won't follow it like it does when you interact with their built in solutions.