Superusers

This branch adds superusers to beLocal! Now, if you sign up as either a vendor or a customer and run `./scripts/addSuperUser.py` with your userID set, you will be added to the system as a superuser, allowing you to activate/deactivate all vendor accounts in the system.

While working on this, I uncovered an interesting bug, which after some consideration, I think may actually be a feature: When a customer signs up, we actually create a Vendor object for them in the database, but this remains hidden due to the user.is_staff flag being set to False. I was originally going to remove this behaviour, but I thought that if we have a customer (who has already liked, say, 30 products) who wants to become a vendor, we should have the ability to turn them into a vendor account (by changing use.is_staff to True) without having to delete and recreate their account. What are everyone else's thoughts on this?

This pull request also includes Carly's M2 UI changes.