Enabling meta learning in Shogun

This page contains the logs of things that have been and will be worked on to enable meta learning in Shogun (collaboration with the ATI).

First part:

• Refactor AnyParameter.h to have a clean differentiation between model parameters (weights, bias,...), hyperparameters (k in KMeans, regularisation parameters,...) and gradient parameters (#4412).
• Refactor SGObject to add all parameters to the new API.