Redis View Counters 2.4.1

Moves some view counters to use Redis-based increment counters rather than scratch tables in MySQL. Redis provides atomic get & del when pushing view counts totals into the database.

Note;

• Currently only handles thread or attachment views.
• There is an effective limit of ~100000 threads that can be updated per 'Update View Counters' cron task run.

Contributing features or bug fixes
Please create a GitHub Pull request via the "Find more info at github.com..." link.