Market hookup

This pull request contains a few market-related changes:

1. Markets are now being pulled from the database
2. There is an updateMarkets.py script that can be run to quickly add markets to your database. To use it, run `python manage.py shell < ./scripts/updateMarkets.py`. If you look at the script, I apologize for how nasty the code for adding markets still is. Writing a more user friendly script is on my list of things to do.
3. Vendors can now join markets via the "Create Location" modal and can leave them via the delete button. It would be great if everyone could verify that the workflow here makes sense. I decided that editing market locations didn't make sense at all, nor did changing a custom location into a market location, so you'll see that you're unable to edit market locations, and if you edit a custom location, you won't see the option to switch to a market location. If this is confusing, we can always change it.
4. Liking has been tested and verified to be working for markets. Thanks Jyoti for hooking this up!
5. Markets are now displaying both on the /vendor page as well as on the /vendor/details/# page.
6. Market card UI has been slightly reworked.

As always, let me know if you have any questions or concerns. If you have a local database on master, you *shouldn't* need to rebuild it.