Show OP_RETURN data on /ordinal

[casey]

If an ordinal is sent to an OP_RETURN output it can never move again, so that feels like a highly significant event. Show OP_RETURN data on /ordinal pages. This will require adding a new table, and possibly will run into #371. We could also see if we can get find fast enough to show the current output on every ordinal page, in which case we don't need a special feature for it.