A read-only property causes misleading exception when omitted as destination property

Omitting a read-only property in a mapper causes a misleading exception:
```
com.remondis.remap.MappingException: The get-method for property 'bruttoGewicht' in type <YADIYADI> is not a valid Java Bean property.
```

An exception that clearifies that a read-only property was omitted, would be better.