Added a check to the initFullImpl() function of the Model to check the "distribution state" of the model.

This check catches a very exotic bug, that can surfaces if the mesh and the model are not correcly initialized.
If the model, i.e. more precice the DOF manager, is created before the mesh was set to ditributed, then some internal members of it, such as the residual or the data_cache are created not distributed.
This leads to problem further down, at least in some cases.

This commit catches some form of this bug, by introducing a check inside initFullImpl() function of the akantu::Model class.
It checks if both the residual and the mesh are either distributed or not distributed.