The outline of the proposal:
- we retain the current fields: contest_{start,stop}, analysis_{enabled,start,stop}
- all timestamps are nullable meaning "extending indefinitely in that direction"
- contest_stop = null => analysis_enabled = False
- analysis_enabled = False => analysis_start = null and analysis_stop = null
- analysis_enabled = True => analysis_start != null
- whenever non-null, contest_start <= contest_stop <= analysis_start <= analysis_stop
(probably the conditions can be simplified a bit, this is just for illustrative purposes)