(PE-1240) Query support for latest-reports events

Prior to this commit, event queries returned all events for all reports.
This adds support for flagging "last-run-only" when querying to return
only the events that came from the latest report.
Cleanup; compound test for last-run-only
Change field to 'latest-report' instead of array
Merge pull request #628 from shakedown/dev/burgundy/pe1240-query-latest-reports

Dev/burgundy/pe1240 query latest reports