typo fixed: change hundt to hund
corrected some ismorphismTest tests not to violate hund's rule
allow up to 2 unpaired electrons for isomorphismTest tests
created permutations of 2 elements, so that element composition can vary too

this way we check whether RMG sees the difference between C and S for
example
make use of Cs atom type for groups

proof of concept, should be extended towards other atom types as well.
added some test in which 'group' atom types are used for isomorphism

we now match 'C' for the molecule against 'Cs' for the groups