[JRO] Update user's messageboard preferences

* Rename Preference to MessageboardPreference. There is a UserPreference model already so a Preference model is a bit too ambiguous.
* User can go directly to the preferences for a specific messageboard
* Change the messageboard helper method to find by id or slug/name instead of just the name.
* Update the authentication page object module to find the first or create a user. Don't create one if it already exists (by name)