Make inner classes static (or seralizable)

Serialization xstream complains when something it tries to deserialize doesn't have a no-args constructor.

Non-static inner classes don't have no arg constructors because the constructor always contains a behind-the-scenes reference to the parent class.

Sometimes serialization xstream can get around that by reflection, but it looks like after a recent Java security update (Java 8 version 222) something has been restricted and this is no longer possible.

The easiest fix for this is to make inner classes static.