GET /api/opportunities takes released_from, an RFC 3339 time, and lists
only the opportunities whose latest release is at or after it. It works
with paging and with changed_after, which keeps the same batch either
way; an invalid value is 400.
The frontend's filter defaults to 7 days, from midnight UK time, and
sends it with every load and catch-up, so a year of opportunities isn't
downloaded to show a week's. Changing the days loads the list again;
Clear filters goes back to 7.
bwilliams
746fa0a9c1