Bugfix: MAC OUI

Since integration of mac module, ethernet OUI was not working.
- new option in netmagis.conf, ouiurl, URL to fetch OUI list
- new table 'oui' and function 'manuf' in mac schema
- awk script to populate mac.oui table (taken from postgres contrib)
- modification of mac cgi to call mac.manuf function
FIXME: write upgrade and maintenance script