add mimetype description for common multimedia file extensions in the default configuration

The current default mimetype configuration in nxmimetype-service.xml does not provide any description:

1- add the missing 16x16 icons to the nuxeo war (one for video files and one for audio files should be enough e.g. the one from /usr/share/icons/gnome/16x16/mimetypes under ubuntu (see attached files).

2- find the official mimetypes for the following extensions:

• avi
• mov
• mpeg
• mkv
• ogg
• ogm
• mp3
• wav
• flac
• aac
• anyother common missing file extension