Move the RExtbans module to its own file

This module should probably be inside its own file like WhoisAccount is, as
it is not related to NickServ in any use, nor does loading NickServ load
this module as well, so it makes sense to separate them
Match nickname case insensitively on register
Disallow autostatus extbans that are higher than the user's current rank
Cache stored modes on channel creation to prevent an override
Remove default modes when a registered channel is created
Remove a user's statuses in all channels when they logout
Merge pull request #83 from Heufneutje/services-fixes

Services fixes