Improve music playlist rendering.

This change:
* bolds currently playing song in playlist;
* forces song names in playlist to one line, ellipsize after (...);
* adds jQuery tipsies to get the whole song name, along with the
  artist name, and the album the song is coming from.

No need to split this changeset into three different ones for the sake
of atomicity.

Two first elements were on the priorities / bug list available there:
   http://gitorious.org/owncloud/pages/Home