Velocity templates should be called for ascenedant primary types

Fix for: https://www.pivotaltracker.com/s/projects/684825/stories/79207804
As I say below, you shouldn't need any loops here, but if you use them, you'll want to use org.fcrepo.kernel.utils.iterators.NodeTypeIterator, not the JCR type, which isn't properly generic-ized.