Added Registrations helper spec

I added tests for the registrations_helper.

registrations_helper_spec.rb is the file I created, and made tests for.
When you think of the `display_email?` method, do we expect it to return a boolean or a boolean-ish value? The test description seems to indicate that you meant `be(false)` though you are using `be_falsey` here. Pick one but be consistent :wink: