Search (for song title, song tag, user)

Search form now searches for songs
- on song title
- on song tag
- on song owner (user)

Additionally there is a new dropdown menu to define the sorting (title,
date, ascending & descending)

When the search matches no results, a message is displayed and the sort
dropdown menu is not displayed.
When the search matches results, a message is displayed ("There is 1
result." / "There are 20 results").
Merge branch 'master' of https://github.com/zyborgLP/bumblr