rename __k_effective_cache -> k_effective_cache in Reaction
rename __k_effective_cache -> k_effective_cache in Reaction

the double underscore makes it private, which is inconvenient, eg
to run unittests for that variable.

pierrelb/RMG-Py,nyee/RMG-Py,nyee/RMG-Py,nickvandewiele/RMG-Py,nickvandewiele/RMG-Py,pierrelb/RMG-Py