Added test cases for Aims

[MatthiasGolomb]

Testcases on Ge for spin-polarised, non spin-polarised and spin-orbit coupling added.

[lucydot]

Hi @MatthiasGolomb sorry for the delay in reviewing this. It looks good though a few changes before accepting the PR:

• is the tests/.gitignore file needed? I think it can be deleted.
• edit the inputs.py module docstring to include new DataAims functionality
• restructure the inputs.py module so that check_data() becomes a module-level function rather than class method. Currently the same method is repeated twice for the Data and DataAims class.

I'm happy to make these changes if you give me permission to push to your fork. I think there should be a tick box option for this next to the pull request.

Thanks for sharing!

[lucydot]

OK, I'm going to go ahead and merge then make the small changes suggested as none of them are critical to performance