Principal::getManyByType now uses same mechanisms as other gets functions

When the internals of the Principal were changed to add getByToken, all the other get functions were updated to use new lookup mechanisms except for getManyByType. This now makes it conform to the others.
Merge pull request #1797 from Dr15Jones/getManyByTypeUsesResolveProduct

Framework cleanups -- Principal::getManyByType now uses same mechanism as other gets functions