Enabled postProcess on film region for reactingParcelFoam

This change enables function objects to be executed on the film region using the postProcess utility/option.

Cross-ref EP 1105

@Prashant

changed milestone to %v2006

added enhancement post-processing labels

The -postProcess mode works. Good to merge.

Thanks @Prashant

mentioned in commit 4678638a

merged

Should actually have been fine to leave this as findObject or even cfindObject. The getObjectPtr just adds a const_cast to the call.

done for symmetry with the non-const version - too many options for this kind of thing at the moment