New save/load system

[Makkkkus]

Is your feature request related to a problem? Please describe. The current system is very delicate, and when adding or removing data with a new version you risk corrupting the whole file.

Describe the solution you'd like We should rewrite the system to use binary or json serialization. This will make the system much more robust, and backwards compatible.

Describe alternatives you've considered Use a library like GSON or similar to serialise/deserialise structured data.