Initial work on adding avatar field; WOrk on #23

rename fields

Work on #23
Updated help text on avatar, WOrk on #23
Merge branch 'master' of github.com:rapidsms/rapidsms.org into feature/23-user-avatar

Conflicts:
	requirements/base.txt
Merge pull request #31 from rapidsms/feature/23-user-avatar

Adding (Gr)Avatar fields