Multimedia file metadata extraction feature

The supported/allowed file type list have been expanded to the
following:

IMAGE (jpg, png, giff, bmp, tiff)
TEXT (txt, rtf, doc, docx, odt)
PDF (pdf)
AUDIO (mp3, wav, aiff, aif, aifc, snd)
VIDEO (mp4, mov, divx, flv, 3gp, wmv, vob)

The database schema has been expanded to include to following metadata:
- file size (for all files)
- playtime (for audio and video files)
- x resolution (for video files)
- y resolution (for video files)

Extraction of metadata for multimedia files is now being supported. For
the time, only the metadata mentioned above are stored in the database.