Initial First Pass of a Session Cleanup Tool

This provides a Tab in the 'Tools' menu that cleans up sessions.

It does 3 things. First does the session clean up like the cron does. Next it looks for sessions that expire greater than 2050 (to cleanup from that bug we had in EDD Session management), and 3rd, it looks for sessions that don't have an expiration entry (in case someone tried to do cleanup themselves and didn't realize there were two entries to remove).