update to pages.php minor exploit

A lot of bans can be removed from a tinyboard database because it isn't limited A staff member could select 100 users all at once with a simple javascript function and unban them all this needs to be limited because a staff member on an image board if they feel hostile they can just remove all bans on the tinyboard site easily without being limited to how many people they can unban at a time, this adds an option to limit it.
update config.php config for unban limit

Adding config and error for unban list when a user tries to unban more users than they are allowed too.
Merge pull request #109 from undido/banlistpatch

Banlistpatch