Several improvements to the reaction generation algorithm.
Several improvements to the reaction generation algorithm.

* If the generated reaction has an ArrheniusEPModel kinetics object,
  convert it to an ArrheniusModel object. Don't do this for other types
  of kinetics objects.

* Sort the reactants and products before checking for existing reactions
  just in case. (For some reason this seems to help -- not sure why.)

* Store reactions from separate seed mechanisms in separate "families"
  in the global reaction dict.

* Allow duplicate reactions within a seed mechanism; disallow duplicate
  reactions between seed mechanisms and between a seed mechanism and a
  group reaction.

* Better printing of new edge species and reactions in
  printEnlargeSummary().

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