Investigate moving away from xml serialization

[adriengivry]

Problem this feature should fix
XML was great in 2003, but since then, many more optimized and easier to read serialization file types emerged.
We should investigate moving to:

• Cereal (JSON but with a C++ serialization layer)
• Raw JSON (with rapidjson)
• MessagePack (msgpack): JSON but saved as binary, fast, better for builds, not human readable

Expected solution
Find and implement this new serialization system.

[adriengivry]

I would lean towards Cereal. And maybe msgpack (on top of Cereal) for builds