Allow 'edit' and 'status_update' calculated states to propagate.

Update test expectations and add further test to explicitly show that we
want the described status from a status update to be propagated to a
preceding response, as well as being filled in in the status update
itself (which is mostly to deal with the case where there isn't a
preceding response). Make those changes to calculate_event_states
Make admin edits affect info_request_event described_states.

Make sure that admin edits changing the described state of an info
request are reflected in the latest_status and status values of info
request events so that the info requests are retrieved correctly in
status-based searches.
Set the calculated state on external requests.

Set to 'waiting_response' on creation, to match the displayed state.
Add task for cleaning up bad request histories.
Comments on described_state and calculated_state

Add some notes on the logic and expectations around
InfoRequest.described_state and calculate_status and
InfoRequestEvent.described_state and calculated_state.