added example cosmo_box_gravity_only_3d

examples/cosmo_box_gravity_only_3d/Config.sh

examples/cosmo_box_gravity_only_3d/L50n32/ics

examples/cosmo_box_gravity_only_3d/L50n32/inputspec_ics.txt

examples/cosmo_box_gravity_only_3d/Masses_L50n32_z0.txt

examples/cosmo_box_gravity_only_3d/Masses_L50n32_z1.txt

examples/cosmo_box_gravity_only_3d/check.py

examples/cosmo_box_gravity_only_3d/create.py

examples/cosmo_box_gravity_only_3d/param.txt

examples/cosmo_box_gravity_only_3d/param_music.txt

examples/cosmo_box_gravity_only_3d/param_ngenic.txt

test.sh