SENSEI-302 Modify request API to allow clients to specify which stored f...

...ields to fetch

This patch reintroduces the fetch stored value flag, and replaces the fetch stored fields flag with a get all stored fields flag and a fields to fetch flag.  It also conditionally fetches fields depending on whether group by is used (since the fields are fetched in the collector when group by is used).  It's an attempt to reduce disk and bandwidth usage

This can be made cleaner; want to get thoughts first, then I can clean up as necessary.

It requires this Bobo change:
https://senseidb.atlassian.net/browse/BOBO-287
https://github.com/senseidb/bobo/pull/16