Add support for multiple emails per fax number

[jtnegrotto]

I think the best way to accomplish this is by pulling emails out into another model and establishing a one-to-many relationship between emails and users. Backwards compatibility is going to be a little weird, because we're using the email as the user's fax tag right now.

Easiest way to move forward is to:

1. Create a fax_tag column on the users table
2. Copy user.email over to user.fax_tag
3. Create a table called user_emails with user_id and email columns.
4. Go ahead and create a user_email for all existing users, with the required attributes.
5. Drop the users.email column.
6. Verify that all pages and actions are still working with these changes.

We'll also want to make sure the wiki page for updating PhaxMachine instances is created and describes how to run migrations. Other than that, users should have to do nothing, and everything should work much the same as it has previously.

[jtnegrotto]

Going to begin the migration of some actions from Sinatra to Rails (#2) on this one.