Release v0.11 - Changes due to legacy removal

[JulStraus]

The following list provides an overview of the individual things that must be removed when moving to version 0.11. All legacy methods below where introduced within version 0.9:

• Remove the function variables_capex including its call in create_model.
• Switch to constraints_ext_data from constraints_data for all create_node functions.
• Remove the function create_link(m, l::Link, 𝒯, 𝒫, modeltype::EnergyModel).
• Remove the function constraints_data(m, n::Node, 𝒯, 𝒫, modeltype::EnergyModel, data::ExtensionData).