Adds advertiser field to user :sunglasses:
Update product registration integration test

Now testing a more specific result.
Add permission locks in application controller

Passing the allow? method to permission instance
Add new matchers and helpers to specs :shit:

Created permit* matcher and sign in helpers to write specs with less
code duplication.

*in the rails cast, the name is allow, however, apparently, this was a
reserved word in the new versions of RSpec.
Create permission model and its respective specs