Add CVX class to optimize module

[dchassin]

Integrate cvxpy as a class in optimize module.

TODO

Coding

• Group data and variable linkage
• Object data and variable linkage
• Global data and variable linkage
• Fix dual variable linkage
• Data type mapping on dynamic set_value
• Properties list on dynamic models
• Powerflow module network linkage
• Unit conversion on static models
• Fast data copy to cvx (no size limit)
• Parametric solver (performance boost)
• Add “status” property inaccurate check
• Add support for “valid-to” variable (?)

Validation

• Finalize the comprehensive syntax tests
• Modify cases to allow check of OPF result
• Create a FD/OPF test case

[dchassin]

Note that we should avoid using global namespace imports.