Filling in the email with users' data

There's a function now to produce an email for any user in the list.
Clicking it will show the template, with name and URL for that selected
person filled in.
Returning user ID on save

Save will now return the user ID that was either added or updated.
Also fixed a notice appearing because the 'admin' field wasn't passed
at all when the checkbox wasn't checked.
Removing obsolete closing
Removing old code

Was used when we were only adding new users. Now we can edit those as
well, hence no point in re-adding, which would change their ID and URL.