CLC-3811 CLC-3160 Simplify caching behavior & keys

https://jira.ets.berkeley.edu/jira/browse/CLC-3811
We've been treating view-as cache differently from real-user cache. Since caching is so core to CalCentral, this has thrown off QA & smoke testing, sometimes in very tense circumstances.

https://jira.ets.berkeley.edu/jira/browse/CLC-3160
Our earliest API feeds were all user-centric & so we naively included the string "user" in our default cache keys. Functionally speaking, all that's needed is an "ID", but the names in the code obscured that.

You're right. If it doesn't look like too hairy a change, this PR might be the place for it.