rebind dynamic entity type - WIP

this refactors the rebind tests, and provides some placeholders for testing persistence of dynamic type info esp effectors

the feature is commented out, but interested in review of it, @aledsage

the refactored tests should be useful for other tests e.g. policies which @grkvlt i think you're working on

(this should be safe to merge, as the WIP is marked; i wanted to make it available ASAP for others working in this area /cc @grkvlt @andreaturli )