Text on account deletion / confirmation

I'd suggest clarification text on the account deletion screen explaining what happens to the username, and what data removal practices are in place at keybase. I assume it is permanently removed from service as per comments on #193, and that all keys and user data are wiped.

Start by reviewing the account deletion screen and the comments on issue #193 to verify the intended username and data-removal behavior. Done means the screen clearly explains what happens to the username and which keys and user data are removed.

Written by the indexing model from the issue text.