Add a timed embargo system

[jirhiker]

@ksmuczynski @jacob-a-brown @chasetmartin
We need an embargo system that will make data permanently inaccessible or inaccessible for a given time period.

Possible solution:
in addition to release_status we should add an embargo_date and embargo_status

After the embargo_date has passed release_status is set to embargo_status

[jacob-a-brown]

We could use embargo_start and embargo_end to set an embargo time period, during which release_status would be irrelevant. After it ends then release_status would be used to control access. That way we won't need to worry about setting release_status after the embargo period is over.

[jirhiker]

That sounds like a better solution

[jacob-a-brown]

If we proceed with embargo_start and embargo_end how should we treat indefinite embargos?

Two possible solutions that come to mind are:

1. Allow embargo_end to be nullable. If it is null then the embargo is indefinite.
2. Set embargo_end to some far-off future date, like the year 9999, so that the time period never ends.

[jirhiker]

1. leaning towards this
2. remember Y2K?