Do not generate a silent assertion for an address in a transition state. Update backend to correctly mark addresses as "secondary" upon verification.

* When calling /wsapi/complete_reset.js or /wsapi/complete_transition.js, immediately flip the type of the email address to "secondary"
* Add explanation of silent assertions.

fixes #3515
Add Selenium tests to check for transition states.
Add backend tests for transition_no_password and transition_to_secondary cases to ensure email type is set to secondary and state changed to known.
Add a transition-to-secondary-forgot-password Selenium test.

This is for a user who has to transition to a secondary but forgot their password.
Merge pull request #3545 from mozilla/issue_3515-silent-assertions

Do not generate a silent assertion for an address in a transition state.