Use classmapping to overwrite 'save' method in importProcessAction

When importing data in Pimcore using CSVImport one cannot use
classmapping to overwrite methods such as save. Say you want to import
some addresses and geocode them at import. One way to do this would be
to create a class called Address (Object_Address), derive a class
called Geocoded_Address, update classmapping.xml, overwrite the save
method with geocoding logic and CSVImport the addresses. With this
patch it's now possible to do this.