Check if data is still valid regarding to model

[jcarpent]

Algorithms can crash if a model is modified after creation of data struct. Add a method to check if a data is still valid regarding to model.

[jcarpent]

It seems that model as a const ref is not mandatory in the Data struct. The idea is to allow a default constructor with the max number of joints (useful for pre-allocation) or with a model. We also need a method with model as argument to build the data struct.

[nmansard]

Solved by #320