UAR 785: Copy custom data from amendment back into main protocol when amendment is merged

Fix consists of calling the ProtocolCustomDataService to copy the custom data from the amendment back into the main protocol, when the amendment is approved and merged.
Note: this fix is located in org.kuali.kra.irb.ProtocolDocument. I expect a similar fix for IACUC since they don't share the code base for the mergeAmendment method.