Flac support

[edne]

Traceback (most recent call last):
  File "/usr/lib/python3.5/threading.py", line 914, in _bootstrap_inner
    self.run()
  File "/home/edne/spazi/airhead/airhead/transcoder.py", line 86, in run
    save_tags(in_path, out_path, uuid)
  File "/home/edne/spazi/airhead/airhead/transcoder.py", line 44, in save_tags
    tags['import_date'] = datetime.now().strftime("%Y-%m-%d %H:%M:%S")
UnboundLocalError: local variable 'tags' referenced before assignment

when uploading a .flac file