UC-111 FB Connect modal; put create and connect existing account all in the same modal

The old version of FB connect displayed a modal when users choose to login via the user menu. This modal allowed them to create a new account, or click a button that would take them to a sign in page. Rather than split the experience, put create and sign-in in the same modal.

https://wikia-inc.atlassian.net/browse/UC-111