[Development] Support for *Notes and UpstreamFiles fields in qt_attributions.json files

[Edward Welbourne]

So I finally found time to look at the JSON specification [0] and find
that (in section 6) it says, of the name/value pairs in an object:
<quote>

The JSON syntax does not impose any restrictions on
the strings used as names, does not require that name strings be unique, 

</quote>
[0] PDF linked from ECMA 404,
https://www.ecma-international.org/publications-and-standards/standards/ecma-404/

It's possible that some JSON linters or tools complain about non-unique
keys, but they're not an *abuse* as such, so we can legitimately go with
the simpler approach Kai has proposed, just one field, Comment (taking
any data as value) will do.

I'll amend my proposed change to QUIP 7 accordingly,

	Eddy.