Style fixes

This pull request:
* Adds padding to the whole #content area
* styles the configuration and media detail sections
* modifies UniverseView to give padding to the search button, and spacing to the playlists, so they take up less space and stack properly
* fixes some inconsistencies in the 'edit playlists' view
I based this branch off of `config-client`, so I am not sure this should be merged there or directly into master after that branch has been merged. I did not merge @josx 's pull request since it seems there were some small things to review.