Changes url for retrieving top tags

Reorganizes the code
Updates API
Implements solo_views API, adds 'options' field to playlist table

Implemented functions:
* list_shared_playlists()
* update_playlist(uid, plid)
* remove_playlist(uid, plid)
* copy_playlist(uid, plid)

Updates the model of a Playlist according to the new 'options' field, and the
schema.sql.
FIX remove_playlist method set to 'DELETE'
FIX parentheses in g.store.find()
FIX NotOneError: one() used with more than one result available (l. 90)
FIX many little bugs
FIX missing 'is' in if statement
Merge branch 'dev/solo'
Added new error to constants