"library" thread
- Implement filescanner as a library_source
- Add library source implementation for spotify
- Move process_media_info to library with small adjustments:
- Remove dependency to F_SCAN_TYPE defines
- Pass data_kind as parameter
- Pass media_kind and compilation as parameter if a source forces a
specific value for these
- Move declaration of scan_ffmpeg to library; add
library_add_playlist_info to library
update db to v19 removing the file extensions from the stored playlists
An existing file extension in the virtual path leads to wrong entries in
MPDroid (and mpd does also not return the file extension).
