Validate vendor location and implement Bootstrap forms

This PR adds functionality to validate that the vendor is located in an allowed area. Allowed locations exist in the user model as self.allowed_locations.

This PR also uses HAML in the sign up page, and uses Bootstrap forms gems to make life less of a headache with forms. Still need to do some grid styling on the forms, I'm terrible at that :smiley_cat: @thejinxters want to help me with that later?

Anyway, let me know if you have any questions about it.