Reorganise SBML folder structure

[stellaprins]

• [x] Reorganize folder structure:
  • [x] Top-level folder should contain: SBML file and SED-ML files,
  • [x] Reorganise the folder structure to improve navigation. Subfolder called tests should contain d1 plots folders, all of the files starting with test_biosimulators_ or test_compatibility, and the results tables.
  • [x] Adjust filepaths in code and GitHub Actions to reflect the new folder structure

[stellaprins]

Changed the folder structure as discussed but still dealing with some permission denied issues when running GitHub Actions.

./tests/validateAll.sh: Permission denied
Error: Process completed with exit code 126.

[stellaprins]

Permission issues solved by adding 'chmod +x' to enable execute permission and using the 'python script_name.py' form.

[stellaprins]

• [x] in GitHub Actions print first few lines of the md table or the size of the md table to check whether the correct output has been created.