CLC-1813 Load required classes from Backstage; HotPlate master does not need to be a Celluloid actor
CLC-1813 Single-thread HotPlate warmups; don't write to UserVisit on every status API hit; add some classes to cache expiration
CLC-1813 Don't expire UserApiController's cache
Merge pull request #1068 from ctweney/clc-1813-async

CLC-1813 HotPlate fixes