XD-732: JSON Property Access

Not sure about the exception to reset cache trick (see eg https://github.com/markfisher/spring-xd/commit/b6e828f4944f4ba5ad358ee35d176f13c695bfd2)

Not sure about whether we want to support write either, and if so, whether to only support write of JsonNode or what I attempted (this has shortcomings, like can't write primitive array). But this code seems very cumbersome, Jackson must have this somewhere...

Also, put that in tuple project for lack of a better place but... maybe in x.integration, given that this story emerged b/c of exposing the EvaluationContext in SI?