Allow users to create accounts

Users will be able to sign up for a free trial of AccessLint Pro by creating an account on accesslint.com. Clearance is being used to handle user auth.

There is currently no link to sign out, as there are no features for signed in users, and therefore no difference between being signed in and being signed out.

https://trello.com/c/WDFJQGlS/32-customer-can-create-an-account
Not crazy about this conditional here because of the repetition and nil checking, but per our conversation maybe it's alright. Up to you.