rebind dynamic entity type

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 )