raven temporal coincidence search for external triggers and superevents

• trigger raven search upon lvalert notifying superevent creation in gracedb; update orchestrator.py
• trigger raven search upon lvalert notifying external trigger creation in gracedb; update orchestrator.py
• need to see what lvalerts look like in either case -- especially for the superevent creation since it has different keys
• create task that calls ligo.raven.search.search method
• create test tasks and files that call raven
• create coincident external trigger and superevent in gracedb-dev1 and run raven.search (this is lscsoft/raven#3 (closed))
• perform annotation on Superevent in case of coincident trigger -- more specifically, call addEventToSuperevent to add to the Superevent's list of em_events in object dictionary