Added support for freeform types

[aaronp]

This changes fixes routes which have freeform types. Previously they were just represented as "Object", and didn't have any default value.

The freeform schemas now are of type usjon.Value, with ujson.Null, to coincide with our cask ecosystem.

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[aaronp]

Howdy stranger! ;-)

@wing328 , please do let me know if I shouldn't be targeting you directly or I should at mention other people/groups.

I just wondered if you wouldn't mind having a look at this?