New UI: boxed

New UI added. No, it won't replace the classic one. No, it will not even be possible for a user to pick the new one. That's still a TODO.

Now about the ui:

The concept is on not having a single song list, but having a playlist and two buffers: one for search, the other for suggestions. Using multiple songlists, it's easier to create more mixed playlist. It's also possible to check what's suggested to currently playing songs and manually picking what it fits.

The idea is that without such a rich interface you end up listening to "whole search results", which is not only boring, but also gives nothing interesting to the markov chain. If the user can play more mixed music, the underlying markov chain will improve, and we will see something funny happening.