Bspline1 include ipopt options argument

In the Casadi 3.6.*, the nlp_scaling_method option of ipopt caused infeasibilities in some models using the BSpline1D class.

This pull request includes ipopt_options as an argument in the fit class method of BSpline1D. Using ipopt_options, the nlp_scaling_method option can be set to "none" by the user to avoid autoscaling issues in ipopt.

This pull request is linked to this issue.

After this merge request, the corresponding models can be adjustes in the test bench. See here.