Speed up get_events_in_database by preprocessing events on backend

[wfehrnstrom]

If my understanding is correct, events_current_processed_collection consists of all events already ready to be served directly to frontend. If this understanding is correct, then we are ```
doing extra work when we are processing these events again, here:

Bmaps-Backend/src/mappening/api/utils/events/event_collector.py

Lines 35 to 39 in 747a4ff

	if one_result_expected:
	# check if it is in eventbrite database
	single_event = events_current_processed_collection.find_one(find_dict)
	if single_event:
	output.append(event_processor.process_event_info(single_event))