Provide a safe mechanism to change attributes in datafits/penalties/solvers

[Badr-MOUFAD]

So far nothing prevents users from changing datafits/penalties/solvers attributes and refitting a model

This might be problematic, especially for

• datafits that require initialization prior to usage
• solvers supporting warm_start parameter

Not re-defining the classes might result in errors and/or erroneous results.
However, this re-definition is less natural, namely for average users, and is subject to oblivion for more familiarized ones.

This issue is to discuss ways of preventing that.