Explore new JSON implementation

[allejo]

Though I doubt that the libjson-c-dev will change names again, the fact remains that it's not easy to use and requires my JsonObject wrapper to make JSON usable.

There's a new contender over at nlohmann/json that:

• is distributed as a single .hpp file meaning it can be dropped in this repo and you'll never have to worry about external dependencies for compiling this plug-in ever again
• allows JSON to be accessed like a first-class data type in C++
• does not require linking in any of our build systems