Use gson instead of fastjson

Comment From: codespearhead

Why not just replace it with Jackson since it's already defined in the parent POM?

Comment From: markpollack

What is the motivation? @tzolov will need to confirm, but we have had several issues with incompatible versions of libraries that different 3rd party libraries requires - in particular at autoconfiguration support is contained in a single project.

Comment From: markpollack

reopen if you can make a strong case for this.