added first draft for getting mass and stiffness jacobian. single_phase_gw/test_single_phase_gw.test_mass_and_stiff_jacobians has simple test that worked
add Diffusion_SIPG_exterior for SIPG weak boundary conditions
periodicDirichletConditions seems to be required for some cases but not in default_n
Revert "added first draft for getting mass and stiffness jacobian. single_phase_gw/test_single_phase_gw.test_mass_and_stiff_jacobians has simple test that worked"

This reverts commit 5b8d6685ee551d9bbae09dabded818d672b9f59d.
Merge pull request #62 from erdc-cm/fix_periodicConditionsFlag_and_Diffusion_SIPG

Fix periodic conditions flag and diffusion sipg