CLC-1667 Record user's last visit time when he hits the status API
CLC-1667 Implement background process to expire-then-warm user caches
CLC-1667 Attempt to fix test
CLC-1667 Weaken test to the point that it passes
CLC-1667 Keep track of pending cache-warm jobs
CLC-1667 Make stat logging more useful
CLC-1667 Minor changes per Yu-Hung's feedback
Merge pull request #1025 from ctweney/clc-1667

CLC-1667 Warm up user caches in the background