correct missing gravity

LDDsimulation/helpers.py

...R-multi-patch-same-wetting-phase-as-RR-zero-nonwetting.py

...ti-patch/layered_soil/TP-R-layered_soil-all-params-one.py

...se-Richards/multi-patch/layered_soil/TP-R-layered_soil.py

...h/layered_soil/mesh_study/TP-R-layered_soil-mesh-study.py

...-layered_soil_with_inner_patch-all-params-one-finer-dt.py

...atch/TP-R-layered_soil_with_inner_patch-all-params-one.py

...ner_patch/TP-R-layered_soil_with_inner_patch-realistic.py

...ayered_soil_with_inner_patch-all-params-one-mesh-study.py

.../TP-R-layered_soil_with_inner_patch-pure-dd-mesh-study.py

...P-R-two-patch-test-case/TP-R-2-patch-pure-dd-realistic.py

...wo-patch/TP-R-two-patch-test-case/TP-R-2-patch-pure-dd.py

...-patch/TP-R-two-patch-test-case/TP-R-2-patch-realistic.py

...s/two-patch/TP-R-two-patch-test-case/TP-R-2-patch-test.py

...test-case/TP-R-2-realistic-parameters-densities-scaled.py

...h_studies/TP-R-2-patch-mesh-study-all-params-one-but-g.py

...se/mesh_studies/TP-R-2-patch-mesh-study-all-params-one.py

...o-patch-test-case/mesh_studies/TP-R-2-patch-mesh-study.py