gemini3d/gemini3d: many bugfixes

bugfixes

• check_finite_output checks on all images, not just root (more robust early failure when a sim doesn't converge)
• correct linking of Mumps-Scalapack-Lapack--remove linking hacks, use modern CMake INTERFACE to eliminate redundant and buggy duplicate link specifications
• improve PyGemini interface robustness to use python -m gemini.<method>
• fix CMake infinite loop when called from MatGemini

• select Fang 2008 (maxwellian) or Fang 2010 (monoenergetic) models
• improve test parallelism