Fix EntityType.name to not say "Impl"

- Previously used entity's getClass().getCanonicalName(), so
  the EntityType.name frequently included Impl.
- Now uses EntityTypeRegistry.getEntityTypeOf to reverse-lookup
  which interface the entity is for.
EntityType.name: incorporate review comments
Merge pull request #535 from aledsage/fix/EntityType-name-notIncludeImpls

Fix EntityType.name to not say "Impl"