Check job pre-run function

[YHordijk]

Added a AMSJob method that is always called before the calculation is run. This is used, currently, to make sure that the initialhessian is not set to DFTB if spin-polarized ADF calculation was requested.

[SiebeLeDe]

I agree to introduce such functionality. We may want to split the _check_job method further if we want to take into account more special cases. Furthermore, we may want to make this a function instead of a method for testing purposes.

Functions are much easier to write unit tests for than classes, especially if the functions are "pure", which means in this case, having the self.settings both as argument and return.

[YHordijk]

I agree to introduce such functionality. We may want to split the _check_job method further if we want to take into account more special cases. Furthermore, we may want to make this a function instead of a method for testing purposes.

Functions are much easier to write unit tests for than classes, especially if the functions are "pure", which means in this case, having the self.settings both as argument and return.

If you want you can open an issue for this and we can discuss what would be the right approach to take here. I agree that pure functions are easy to test, but I also think it fits the purpose of a class method.