- Support #528, #370, #551, #285, #115: various cleaning-up in the code (canonical form for classes, final keywords, more appropriate smart pointers for each class and so forth...) - Bug #547: Fix compilation bug in XCode for release mode. - Support #545: VariationalFormulation: merge DefineOperators() (previously required by the CRTP of the base class) within SupplInit(). - Feature #511: Create a Stokes operator and use it in Stokes model. The previous instantiation of Stokes can still be used with the macro STOKES_MODEL_WITH_TWO_OPERATORS activated (an XCode target has been created for that purpose). - Design #537: Implementation of the local variational operator GradPhiGradPhi has been improved.