SW-15 (Mapper) Exception is thrown when user is mapping nasted properties

See issue #23 

For nested mapping use additional annotations as follows:
``` java
@MappableTo(StudentSnapshot.class)
public class Student extends Person {
	// single nested mapping corresponds to StudentSnapshot.setStreet( Student.getAddress().getStreet() );
	@MapNested(fromNested = "street", to = "street")
	// multiple nested mappings are also valid
	@NestedMappings({
		@MapNested(fromNested = "city.name", to = "address"),
		@MapNested(fromNested = "city.population", to = "population")
	})
	private Address address;
}
```