Integrate and encourage new account creation

When people write their first issue or comment, they might prefer to have a gitlab account—and an issue or comment is a much better "audition" for a gitlab account than our current "why do you want to help with Tor" text field on the account sign-up page.

As part of making an issue or comment, we should encourage people by default to pick the account name and signup info that they would like to have. On the admin side, we should make it easy to "approve comment and account request", with "approve comment only" as a rarer option.