Making apache server-status optional with a marker

Apache server status won't be enable by default. User will have to add `public_server_status` marker to enable it. This will also apply on the `ExtendedStatus` option. 

Based on Trello card:
https://trello.com/c/R0H10FIH/22-make-server-status-user-configurable-via-marker
If this 'enable' something, we should call it:

`enable_public_server_status`, thoughts?