(PDB-718) Fact path endpoint

This implements a "fact-paths" endpoint that returns list of fact paths/types
according to the specification here:
https://docs.google.com/a/puppetlabs.com/document/d/1vWE6tBmsPmMIYKQWV8Pwes_NIR9lEMTYjUH8zJ_AlMI/edit?pli=1
Well no it isn't is it? :-).

I'm not even sure you need this case statement to be honest. I know we do it as a catch, but I'm not 100% its needed here if we are already absolute about it in the upstream routes.