Allow for null Release Date

Currently the release date field is required. But usually when a release is first written up there is no realistic idea for when it might be delivered. For releases that are postponed or of lower priority, the initial entered dates which seemed so far off and realistic at first, even 6 or 12 months out, well, someday those dates arrive. And then reports get clogged up with "imminent" projects that actually haven't even been started.

It would be helpful to allow for null release dates so nobody looking into Aha gets accidentally fooled into thinking something is going to arrive that date.