unify our PATCH value representation/handling

[joel-bluedata]

There are now multiple spots in our code where we do a PATCH, and multiple ways in which we handle defining a data structure for the PATCH payload, sometimes with an auxiliary data structure and custom JSON marshalling.

In cases where the PATCHed value is a pointer to a primitive type (bool, string, int) we could have a common data structure and marshalling that is used by everyone. It is probably time to refactor our code to do this, rather than continuing to have each instance of a PATCH doing a roll-your-own solution.

[joel-bluedata]

Depends on issue #194.