[ticket/12150] Add options to acp

PHPBB3-12150
[ticket/12150] Add prune columns to schema files and migration file

PHPBB3-12150
[ticket/12150] Add file and caller for pruning shadow topics

PHPBB3-12150
[ticket/12150] Add missing prune settings variables in acp_forums

PHPBB3-12150
[ticket/12150] Add missing space to query for shadow topics

PHPBB3-12150
[ticket/12150] Add functional tests for pruning shadow topics

PHPBB3-12150