Add Seafile Support

From Google Groups (https://groups.google.com/forum/#!topic/clementine-player/pNqwtNUfbv4) : 

"I was very happy and found that was a very good idea to add to Clementine cloud storage services support.
But there are only private services (Dropbox, Google Drive...) and I personally use Seafile (for downloads : http://www.seafile.com/en/download/), which is a free software and could be installed on our own server. It's a Dropbox like."