Adding support for BugMeNot's "Other" field

[dizzy-egg]

BugMeNot often provides a third credential field, "Other", which usually contains email addresses used to sign up to the websites.

These changes allow the "Other" field to be pulled through to the extension.

Example website to test with: https://greasyfork.org/en/users/sign_in

Note: some BugMeNot submitters might include email addresses in the first ("Username") field and usernames in the "Other" field, so this won't work perfectly every time.

It would be useful to include some logic which tries to determine if the data in a field looks like an email address and if so it tries to insert it into the relevant "email" fields.

[vantezzen]

Look great, thank you for your contribution!

[dizzy-egg]

Thank you for creating the extension!

My edit does need some improvements though. I'll try to add some kind of logic which handles usernames vs. emails, as I said. I'll let you know when I do.