Fixed bug of mutating reactionDict list, causing large memory spikes.
Fixed bug of mutating reactionDict list, causing large memory spikes.

Due to extending my_reactionList with ownReverse reactions, we were mutating
the reactionDict on accident.  This led to my_reactionList having billions of
reactions when there should only be around 10 reactions.  We saw huge
memory spikes due to this.

nickvandewiele/RMG-Py,faribas/RMG-Py,pierrelb/RMG-Py,nyee/RMG-Py,comocheng/RMG-Py,KEHANG/RMG-Py,comocheng/RMG-Py,chatelak/RMG-Py,enochd/RMG-Py,nyee/RMG-Py,nickvandewiele/RMG-Py,enochd/RMG-Py,chatelak/RMG-Py,KEHANG/RMG-Py,pierrelb/RMG-Py,faribas/RMG-Py