CLC-4181 API to let superusers delete specific cache entries

https://jira.ets.berkeley.edu/jira/browse/CLC-4181

This will assist our standard upgrade procedure and should also help when diagnosing or working around certain production issues.
Reading the docs for Rails cache it seems that force has an effect on the fetch and the write methods, but nothing is mentioned for delete. Does removal of the :force option change the behavior in any way?