Features/setup new module structure

[jnnr]

• [x] Fix error importing cartopy

TODO

Structure

• [x] Setup general structure sketched in #14
  • [x] Do consistency checks
  • [x] Assert that required parameters are defined
  • [x] Set default values
  • [x] Models and results

Clean up

• [x] Write docstrings
• [x] Add module headers
• [x] Render components and components_attrs in docs
• [x] Check if examples are working
• [x] Fix failing tests and linters
  • [x] Fix error on installation when installing rtree