- Update Petsc to v3.11.3. - Update Openblas to 0.3.6 - Revert to Boost 1.67: versions 1.68 and 1.69 get issues (missing symbol in 1.68, and ill-designed modifications in hidden symbol options in 1.69 that breaks runtime of MoReFEM and issue a link warning I didn't manage to solve). - Update Openmpi to 4.0.1 - Add explicitly -stdlib=libc++ in CXXFLAGS for all libraries to avoid conflicts between libc++ and libstdc++ (the issue was probably here before but led to a compilation error due to a difference of signature in <variant>). - Separate Fedora Dockerfile to limit the size and not install both compiler (only a half success: clang package installs gcc currently as dependency...) - Modify the Dockerfile to capitalize on the recent Docker option --squash to reduce image size dramatically. - Now that Petsc supports Python3, remove all occurrences of Python2 and use the Python3 everywhere (simply named Python).