[4.x] Add some feature tests

[joelbutcher]

This PR adds a feature tests file to the unit tests for the package to ensure the following features continue to work:

1. The OAuth redirect behaves as expected
2. New users can register
3. Existing users can login
4. Authenticated users can link to a provider
5. New users can register from the login page
6. Existing users can login from the registration page
7. Socialstream generates emails for providers that return missing emails