cosmetic improvements on gazette admin
refactored freebase entries downloader so:
  - it works on py3
  - it returns the download entries instead of storing them on file
  - cleaned up some repeated code.
using new api of freebase downloader
new field on gazette items, and some admin improvements for them
removing uniqueness to field
adapting gazette loader script to work also on freebase downloading mode
error handling for freebase downloader
Merge branch '421-add-gazetter-from-freebase' into 330-gazeteer