Application and Thing Registries may be needed

[james-martin-jd]

It seems when building something like a POD manager, quick access and searchability of all Things in the POD and all Apps registered to the POD is a necessary ingredient. Right now, there's no dedicated registries for these items. TypeIndex might be usable, but it seems like it would be good to split these out into separate registries.

They would need to also include private and public indexes as well.