Prefix Essentials featuring auto expiring prefixes and prefix filtering 2.3.6.1

• Performance fixes when a large number of threads exist on a prefix
• Implement short caching of thread totals per prefix as this can be quite slow
• Simplify viewing a list of threads for a prefix to only show visible threads (even if the visitor can see deleted/moderated threads)

Add caching to avoid performance impact of counting prefixes & threads every page load

Bug fix for an error in 2.0.3

XF2.1 compatibility update

Ensure latest thread prefix in forum list is updated when a thread's prefix is update

Fix saving a 'new posts' filter as the default filter

Just a tidy up and now out of beta