Separation of eddy/bolus velocity contribution to MOC from mean

[milenaveneziani]

This is two issues in one:

1. once the MOC online accounts for the bolus velocity contribution when GM is on, we should remove the temporary config option usePreprocessingScript. See also issue Account for bolus velocity in MOC AM when GM is turned on MPAS-Model#55;
2. we should visualize both the mean and eddy-induced MOC streamfunction.