add `branch.py` script for initial email burst
limit the number of email addresses
remove leftover test fixture
remove email_address_with_confirmation
notify users who don't have a verified email address
fix i18n in `verify-email.html.spt`
make the `website` object available to the DB model classes
split some i18n functions for reuse in `Participant.send_email()`
implement email i18n
move email methods under "Emails" heading instead of "Random Junk"
set `email_lang` when adding or verifying an address for the first time
improve test coverage