Email Validation

## In this Pull Request

### Email Validations

* Included email validations in the User and Customer model that test for the inclusion of the @ and . (followed this blog post: http://davidcel.is/blog/2012/09/06/stop-validating-email-addresses-with-regex/).
* Added two test that covered those scenarios, one in User model spec and the other in Customer model spec.

### PS

* I tried to pull the other validations that Laura previously wrote but I don't think I have them on my copy of the previous app. Still, I think these validations might be suffice.