Add a service to map a list properties from a source doc to a target doc

The service exposes a method :
void mapProperties(DocumentModel sourceDoc, DocumentModel targetDoc, String mappingName);
where the mapping is contributed as :

<mapping name="mappingExample">
  <property path="dc:title">dc:title</property>
</mapping>

For the initial implementation, will assume that the source property is mapped to a target property of the same type and that all the properties exist on schemas on the target document.