Merge in changes from master branch for forbiddenStructures.py.

Added in groups for nitrogen added by Beat.  Also addition of singlet
carbene along with the triplet forms.
Manual merge of 1+2_Cycloaddition groups.  Added imodogen to groups.

Allowing nitrogen on all children of multiple_bond (which was split into
mb_carbonyl, mb_db, and mb_tb).  Also retains changes from RMG-Java
for disallowing 2T in carbene groups.  See
https://github.com/GreenGroup/RMG-Java/commit/abee4d8773a785bad189e2558f5200101d70311b
for more details.
Manual nitrogen merge for 1,2_Insertion family.

Retains Beat's changes from commit 99f546a3
Manual merge of nitrogen groups to 1,3_Insertion_CO2.

From original commit 13d3b96390
Manual merge of nitrogen changes to 1,3_Insertion_ROR.

Original commit 425f56b9
Manual nitrogen merge for Birad_recombination family.

Original commit 047ef3ea8
Manual merge of nitrogen changes to Disproportionation family.

Original commit 24ec3302
Manual merge of nitrogen changes to HO2_Elimination_from_PeroxyRadical

Original commit 2135d900aa1
Also fix to mistranscribed rate by Aaron.