Implement backend for browse view
Add browse view skeleton

Styles and control scripts are in place; currently the browse view simply
displays a static list of all artists.
Add second level (albums) to browse view
Implement third level of browse view: songs

Clicking on a song reveals detailed song information. Clicking on it for the
second time adds it to the playlist.
Songs are added via MPD's findadd command only by searching for the song title,
which could prove to be quite sloppy. Maybe the artist should be considered as
well.
Non-ambiguous adding of songs in browser view

Songs are now added by first searching all song with the given title and
filtering the results by artist and album.
This completes issue #17.
Merge pull request #24 from haggl/browser-view

Browser view