Fixed a potential infinite loop during missing group generation.

In particular, during the step where the code is searching for all child nodes that are subgraph 
isomorphic to a newly generated group, the function for isomorphic checks may misidentify two graphs as
 isomorphic even if their labeled atoms do not match. This will cause an inifinite loop where no matter 
how specific a newly generated group is, there will always be a child node that is subgraph isomorphic
 to it. This is resolved by turning the generate_initial_map option on.

scripts/fitThermoGroupsFromThermoLibrary.ipynb

@@ -528,7 +528,7 @@
     "                                        group = make_group(atom, n_degree_neighbor=n_degree_neighbor)\n",
     "                                        group_str = make_group_name(atom, n_degree_neighbor=n_degree_neighbor)\n",
     "\n",
-    "                                    while any([(group.make_sample_molecule()).is_subgraph_isomorphic(child.item) for child in node.children]):\n",
+    "                                    while any([(group.make_sample_molecule()).is_subgraph_isomorphic(child.item, generate_initial_map = True) for child in node.children]):\n",
     "                                        #Child-node can't be the child of other children\n",
     "                                        #to avoid ambiguous group selection\n",
     "                                        n_degree_neighbor+=1\n",