Release v0.10 - Changes due to legacy removal

[JulStraus]

The following list provides an overview of the individual things that must be removed when moving to version 0.10:

• Remove legacy constructors in src/legacy_constructor.jl and ext/EMIExt/structures/legacy_constructor.jl. We introduced them quite a while ago and I think after 1 year, it is reasonable to remove them, especially given the major changes related to the model since these versions (Version 0.6 to 0.9 in EMB and 0.5 to 0.8.1 in EMI).

[JulStraus]

I will move some of the points to 0.11 breaking change as I personally think that the we should keep the backwards compatibility in EnergyModelsBase for at least 1 additional version increase. Points 1-4 were all introduced within EnergyModelsBase v0.9.