Model test: merge to main

[lucascondeixa]

Main features implemented:

1. Aggregation feature through aggreg.jl
2. New folder structure
3. Bridge between clusters weight and optimisation model
4. Thorough revision of the model

[FabsOliveira]

@lucascondeixa, could you propose fixes to the conflicts in src/io.jl? You have made some significant changes there, so we need to make sure those still hold.