[tim] reworking calculate flow for 1) no longer saving samples to database 2) no longer double completing interval_samples 3) filling reservoir and calculating summaries in the correct order 4) easier understanding
[tim, eric] - No longer save samples to mongo except summaries. Refactored workflow of completing samples and standard deviation. No longer doing multiple saves to mongo
[tim, eric] adding tests around standard deviation memoization
[tim] cleaned up summary find/create logic to hopefully prevent duplicate summary creation
[tim] bumping spec
[tim, eric] simplified summary accessor