xF2 Add-on AndyB Forum list count 1.5

Forum list count v1.5 changes:

Fixed null condition error.

Thread view count v1.7 changes:

Now works with PHP 7.4.

Forum list count v1.2 changes:

Updated setup to use schema manager.

Forum list count v1.1 changes:

Fixed PHP variable which gets the the Limit from the options page.