Revamp default config for some changes going on in the router project.

- Renames "proxy" to "gatekeeper" in the yaml config (so the descriptor
  in the more general router project makes more sense).
- Standardize more of the yaml to snakecase, since that seems to be what
  we're doing for yaml.
- Remove some config settings that no longer make sense (for stuff that
  got moved into the router).
Fix so wildcard host apis still match when a hostname match is present

Previously, the internal wildcard matching for the API Umbrella APIs
was only matching as long as an api didn't exist for the hostname being
used. But as soon as an api was added with the hostname being used, then
all the internal API Umbrella APIs broke, since they were using the
wildcard matching.