Merge pull request #2590 from endJunction/RMMassLumping

...rj/processes/process/RICHARDS_MECHANICS/t_mass_lumping.md

...sLib/RichardsMechanics/CreateRichardsMechanicsProcess.cpp

ProcessLib/RichardsMechanics/RichardsMechanicsFEM-impl.h

ProcessLib/RichardsMechanics/RichardsMechanicsProcessData.h

ProcessLib/RichardsMechanics/Tests.cmake

...a/RichardsMechanics/RichardsFlow_2d_small_masslumping.prj

...chardsFlow_2d_small_masslumping_pcs_0_ts_0_t_0.000000.vtu

...sFlow_2d_small_masslumping_pcs_0_ts_104_t_2000.000000.vtu

...rdsFlow_2d_small_masslumping_pcs_0_ts_19_t_318.000000.vtu

...chardsFlow_2d_small_masslumping_pcs_0_ts_1_t_1.000000.vtu

...rdsFlow_2d_small_masslumping_pcs_0_ts_29_t_518.000000.vtu

...chardsFlow_2d_small_masslumping_pcs_0_ts_2_t_3.000000.vtu

...rdsFlow_2d_small_masslumping_pcs_0_ts_39_t_718.000000.vtu

...chardsFlow_2d_small_masslumping_pcs_0_ts_3_t_8.000000.vtu

...rdsFlow_2d_small_masslumping_pcs_0_ts_49_t_918.000000.vtu

...hardsFlow_2d_small_masslumping_pcs_0_ts_4_t_18.000000.vtu

...dsFlow_2d_small_masslumping_pcs_0_ts_59_t_1118.000000.vtu

...hardsFlow_2d_small_masslumping_pcs_0_ts_5_t_38.000000.vtu

...dsFlow_2d_small_masslumping_pcs_0_ts_69_t_1318.000000.vtu

...hardsFlow_2d_small_masslumping_pcs_0_ts_6_t_58.000000.vtu