Add ability to group metadata

[marthacryan]

Fixes #789. Using an optional "category" field in the "uihints" of a schema, adds a header when a new category encountered.

First pass relies on order of schema properties to determine where to add the headers - planning to incorporate some sorting to make that less reliant on JSON ordering.

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[ajbozarth]

Ran it locally and it works, included some review comments below, but I have a small issue with the implementation, it feels more like a "hack" to support the previous implementation (not that it's not a decent working solution). You create an array of categories then create a list of fields that is created by adding fields matching each category one by one. The idea I had in mind during the previous call was a bit different, rather than having two lists it would be one dict. the dict would use each category as a key with each value being the list of fields. This would then combine the two for loops in your code to just one loop. (This is just my opinion, the implementation here is ok and I would be ok with merging it as is, pending my comments below)

[ajbozarth]

I believe we do something similar to this in renderField might be worth updating that to remove any redundant code.

[vabarbosa]

thanks for the quick updates

[ajbozarth]

Some followup review based on your latest updates. I'll also test it locally but I expect it'll work the same as before

[marthacryan]

Just pulled in changes from #885 to make sure they're compatible with these changes.

[ajbozarth]

Tested locally and LGTM