restrucutre CAD examples

[shimwell]

change CAD examples to a slightly different layout

• task_15_making_dagmc_surface_mesh_geometry_from_cad
  • task_0_what_is_surface_mesh_geometry.py
  • task_1_converting_step_files.py
  • task_2_converting_cadquery_objects.py
  • task_3_converting_paramak_objects.py
• task_16_dagmc_material_tally_fast_flux
  • task_1_simulation.py
• task_17_dagmc_structured_mesh_tally_heating
  • task_1_simulation.py
• task_18_making_dagmc_unstructured_mesh_geometry_from_cad
  • task_1_converting_step_files.py
  • task_2_converting_cadquery_objects.py
• talk_19_dagmc_with_csg_geometry_simulation
  • task_1_paramak_geometry_with_bioshield.py

[shimwell]

paramak needs a bit of a rewrite for some of the tasks

[shimwell]

I've got some examples here which can be converted to jupyter notebooks
https://github.com/fusion-energy/paramak/blob/main/examples/tokamak_unstructured_mesh_simulation.py
https://github.com/fusion-energy/paramak/blob/main/examples/tokamak_structured_mesh_simulation_with_CSG_bioshield.py