Introduce a new set of UniqueEntityLoader impls that use LoadPlan/LoadPlanAdvisor from within EntityPersister. This is intended just as a temporary change to proof the concept of LoadPlanAdvisor as means to handle JPA 2.1 entity graphs. Hooking this into UniqueEntityLoader gives us a chance to verify that the concept works well in practical application without having to completely rip out Loader just yet.