List cases where cacheing is good vs bad in the resolver

We need to establish a cacheing policy that is safe and explicit ( and tested )

• Don't cache any try-it-out or arbitrary requests
• Cache http requests within a single resolver invocation
• Allow holding onto a cache across multiple resolver invocations ( ie: external cache management ).

ping @fehguy @webron @buunguyen please ensure the list above it accurate. Once it is we can implement the tests ( and the implementation too ).