Change "Hide Non-Persona logins" to "Disable Non-Persona logins"

Non-Persona logins can now be completely disabled.
Allow new user registration with Persona.
Remove the paypal link
General cleanup
Disallow password resets if BrowserID only auth is selected.
Clean up the redirection and debug code.
Unify all of the error handling into Handle_error
Cleanup up the assertion checking
The remote verifier checks for assertion expiration.

Checking the expiration date here can cause a verification failure if the local server has clock skew from the Persona servers.
Clean up how to get an assertion, Handle_login, etc.
The Handle_* functions now take an email instead of a result
Remove the auto-create users feature, I am not happy with its security implications yet.
Do not show the password field in the profile page if in BrowserID only auth mode.