setup done -> compose encrypted email should take user to gmail

[tomholub]

#1621

The compose encrypted email green button should take users to gmail & open secure compose, not just take them to settings.

This is a bit tricky because if user actually is logged into more than one Gmail account, it's not obvious which link to open, because gmail differentiates different accounts by number:

https://mail.google.com/mail/u/0/#inbox
https://mail.google.com/mail/u/1/#inbox

I wonder if we could just load these links with ajax one by one, increasing the integer, and parsing the contents until we find the right account. Then open tab for user with that link, and have a secure compose window opened inside it automatically.

[tomholub]

Turns out this works https://mail.google.com/mail/u/some@email.com