Handle "out of template" atoms of molv3000 in KET-format

**Background**
There are cases when monomers in the molv3000 are connected to generic atoms located in atoms ctab.
This case should be handled in KET-format. (See rendered PNG-example)

**Solution**
There are two possible solutions for solve the issue

1) save these atoms into mol0 -> atoms block of KET format and address them as atom_N from connections block, where N is an atom index
2) convert the atoms into CHEM monomers