deps/nlohmann_json, deps/rbdl, deps/sciplot: Add several third party libraries

Changelog entry: New modules sciplot, rbdl and nlohmann_json

At some point, we might remove the versions of rbdl and nlohmann_json from Simox. At the moment, I am preparing some CMake options to have both possibilities. The version of rbdl and nlohmann_json are newer than the ones in Simox. At least the build runs through. Further investigation is needed to validate these versions.

Sciplot is being used in RobotAPI (ukfm test) and navigation (some tests).