(PDB-772) Modify the facts endpoint to return structured facts

This pull request causes the v4 facts endpoint to return typed and structured
facts while leaving the v3 responses stringified as before.  It also adds a
"name" column to the fact_paths table representing the first element of a
fact's path.  This column should be renamed to "fact" in the future to avoid
confusion with the many references to 'certname' as name.
the facts version needs to use a different predicate and to be aware of the API version so the outputs can be stringified on the lower endpoints, but it would be easy to generalize.  Lines 70-71 can go.