Add Observer. Remove functions from python side and add as observer of Problem. Add loads directions as functions. Minor changes.

Add interface for linear sovlers. Add macros definition at global level. Adapt modules to test the different linear solvers.

Various fixes for msys2 (windows) build. Rm mpi4py mandatory dependency. Rm catch by value and uninit build warnings for gcc9. Updt onera mesh size for greater robustness.

Solver and MshDeformation are now responsible for checking negative Jacobian (was Mem before). Add Mem base class and refct derived MemTri3 (pure cpp). Refct Gauss and derived classes. Adpt Element and Tri3. Add namespace in fwk.h

(to be continued)

(see commit a52a375d)

Each module now finds its needed pkgs. Suprsd output in FindMUMPS. Re add sph tests. Rm MUMPS dependency of tbox.