Added Artist, Albums and Songs tabs to the library.

So far, the Songs tab is the only one that works correctly (for the most part).
The Artist tab shows a list of artists, but you can't do anything with it yet
(and it looks pretty bad). The Album tab doesn't do anything at all so far.

The add to playlist button is broken on the Songs tab, but that should be an
easy fix (should).
Fixed the add to playlist buttons not working.
Styled the Artist list.
The artist page more functional now.

It now takes you to an album view of the artist. Which is of course very ugly.
Styled some more
The Ablum tab works

Turns out I had already done most of the work for it...
The Artist tab works.

It's pretty much complete now. Some styling would probably be good. Besides
that, we should have the title div have a click listener to go back to the
artist page.