Namespace AuthGrove\Models

Summary:

• In a next change, we're going to have an UserExternalSource class.
• D27 offers to add an Identity class.

To avoid to flood the app/ folders, we sort them in a Models namespace
and folder.

Test Plan:

• Run tests
• Run db:seed, account:dump, account:info, account:reset CLI commands
• Manual register, reset password, login tests

Reviewers: dereckson

Differential Revision: http://devcentral.nasqueron.org/D430