#31 Object serialization

[Robert]

Currently BeanKeeper does not support serializing a stored object/bean for following reasons:

1. The object will have specific BeanKeeper objects in it, like MapImpl, ListImpl, SetImpl. These need to implement the Externalizable interface to work.

2. When the object is deserialized, BeanKeeper will not know it, because it will lose it's persistenceId. BeanKeeper should check, that if an object implements the Serializable interface, it also should contain the persistenceId, so deserialization will restore the id too.