slow but steady progress the mixxx api is quite

Slow but steady progress. The Mixxx API is quite pleasant to work with so-far. This is only a mock view, the integration with libspotify has yet to happen.

I will likely follow some other feature template that requires linking with an external library, such as Shoutcast + libshout. I pick that example because I know of a UI element that toggles its settings; I can search on whatever setting keys is modifies and find where any key is read. From there I can see the actual libshout integration points, and search back to find any startup/shutdown code.

Once I have a good feel for the integration tasks required, I will follow the plan I form to integrate libspotify into the SpotifyFeature plugin.