deprecate AbstractBaseJavaEntity.parent

The usage of this interface is confusing and in some cases even wrong. The implementation tells us that only a JavaSource or a JavaClass could be a JavaClassParent
But the AbstractBaseJavaEntity has a void setParent(JavaClassParent) and a JavaClassParent getParent(). This would mean that even JavaParameter has these methods, which is very unusual since the parent of a JavaParameter is always a JavaMethod. The getParent() would return something unexpected.