New undocumented property in IdP v5.1.4

[Cantor, Scott]

> I added to the properties reference page

The reference was more or less aborted a while ago, or at least never completed, I was trying to work out some way to deal with this sort of thing.

I added it to the release notes at least for now while I figure out a better place to put it.

Long term, it's my thought that we could build in a way to define parameters and their descriptive info into the software somehow as a data dictionary, and we could essentially have the IdP spit out its own documentation (in this limited sense).

-- Scott