Add Fumili minimizer

[AdrianDBS]

This minimizer seems to be custom-tailored for least squares problems, but offers superior performance there.

[AdrianDBS]

We should update Minuit2 to the latest version before starting the implementation, since recent changes have introduced a common base cost function.

Was a misunderstanding from my side. Although FumiliFCNBase inherits from FCNBase, Fumili has a different way of interacting with cost functions compared to the generic minimizers.