not able to edit a user without a username

[willosof]

Actual behavior

If the name is blank, you won't be able to administer the user settings for a user.

Expected behavior

You should have an edit user-button that one could click even if the username is blank

Steps to reproduce the behavior

1. Clear your GitHub "real name" field
2. Log in via GitHub oath
3. Try to edit that user from admin

Relates to #503 and is more or less a duplicate, but I think that is another issue/approach entirely.

1. Github auth provider should never provide a blank name, if the realname is blank, use the username instead. In that way, it's never blank
2. Add an edit button for the freak accident cases

Cheers