add roles to the admin interface to receive/not receive reminders

Issue Summary

We have a role to which we assign specific individual users and for which we do not want to send email reminders to. It would be great if, in the admin settings, we could select (tick) which roles we wanted to get the reminders.

I am not an expert so I couldn't hack a 'select role' into the admin front end but I imagine for an expert it might not be so hard.

Instead I have had to hack the module (around line 181-ish) so the select statement adds the relationship to the users_roles and then users_roles.rid <> X where X is the users_rol.rid we do not want to be emailed a reminder.

HACK =
... FROM ({users} u INNER JOIN {account_reminder} ar ON u.uid = ar.uid) LEFT JOIN users_roles ur on ar.uid = ur.uid WHERE u.login = 0 AND u.uid <> 0 AND u.status = 1 AND (ur.rid<>X or ur.rid IS NULL)", time());
...

Otherwise this works fine for us = thanks for the useful module.