Bug 1052195 - Select sole verified email by default in the signup page

[adusca]

This will only affect the sign up page for users that don't have a
public email in their github profiles. The default is still the public
email for users that have one.

This also doesn't change anything for users with more than one verified email,
but it would be easy to select one of the verified emails by default.
What do you think is best?

[groovecoder]

IIRC, @stephaniehobson pointed out that if the user has more than 1 verified email on GitHub, we should leave them the option to select whatever.

But, maybe we can default the radio box to their primary email address on GitHub?

[groovecoder]

@adusca - since this is adding extra logic, how comfortable do you feel adding a new test (case?) for the SignupView and specifically for the get_form method? If you're not, I can take that on to make sure we have adequate test coverage here.

[adusca]

I just added a new test case, as we discussed on IRC.

[groovecoder]

Looks good! A potential follow-up is to de-select an email if it's already in use by another account. But that's probably an edge case for those of us who have multiple emails associated with both GitHub and MDN. :)