Add `skipOnFail` option to the `Calculator` to continue featurization/calculations on individual fails

[amkrajewski]

One of the usecases of pySIPFENN is to featurize 100/1000/10000 atomic structures. If one of them fails, this fails the entire calculation. We may want to include an option to proceed and return 99/999/9999 remaining ones, if user explicitly specified to ignore failing ones.