Duplicate account check 3.0

Duplicate account check v2.0 changes:

Updated code used to get IP address.

Duplicate account check v1.9 changes:

Fixed issue dealing with intermittent duplicate entry error.

Duplicate account check v1.8 changes:

Corrected issue with Exclude usernames in the Options page.

Duplicate account check v1.7 changes:

Fixed issue where deleted accounts would still show as duplicate.

Duplicate account check v1.6 changes:

Now using finder for performing database queries.

Duplicate account check v1.5 changes:

Updated setup to use schema manager.

Duplicate account check v1.4 changes:

Cron entry now runs every 4 hours.

Duplicate account check v1.3 changes:

Fixed issue with Exclude usernames.

Duplicate account check v1.2 changes:

Added code to ensure only checking for duplicate accounts if the user_state is valid.

Duplicate account check v1.1 changes:

Username in email is now a link.