Make plan for `nosnoc_py` modernization

[apozharski]

Currently nosnoc_py is quite behind core nosnoc in terms of features. As such we need a plan to move forward with its modernization. In particular we have a two main questions to answer with regards to design goals:

• Create a feature list (preferably using github issues, and perhaps github projects) which will bring nosnoc_py in line with the state of the art.
  • I believe this needs to happen regardless of anything else we decide so I will start on it ASAP
• How to do index tracking? There are currently two main options I see: using casADi structs, or implementing vdx style index tracking in python. I mildly prefer the latter as it would make the implementation similar between python and MATLAB.

@nurkanovic (and @FreyJo if you have input though I know you are busy with acados) I would appreciate some quick feedback and you can add further points if you have them.