Initial Salesforce model and test for Django ORM.
Add empty choice to availability.
Don't let anonymous users update user profiles.
Add location to profile API.

BB-390
Skip Salesforce tests when a salesforce database is not configured.
Merge pull request #363 from benkonrath/more-settings-and-profile-tweaks

More settings and profile tweaks
Merge pull request #364 from benkonrath/salesforce-integration

Salesforce integration