This change includes:

- Improve the spec coverage for incoming request to the webfinger action
- For requests without an accept header (ie, what a browser might look like),
  return a JSON response.
- For requests with an explicit format of xml or json, return that format.
- For requests using an accept header, return that format.

Also adds failing spec showing webfinger does not return xml, which covers the
issue described in: https://github.com/tootsuite/mastodon/issues/1983

* Add locale spec with failing locale plus region check

* Use a more accurate locale when supplied by browser headers

Previously we were using a matching option which would use the first locale
available which matched the locale portion, even if a region was specified.

This changes to first try to find an exact match, and then fall back to the
region, and then fall back to the  default.

* Clean up default_locale method

* Add request spec for host meta route returning xml

* Add routing spec for xrd routes

* Update well-known routes

* Move webfinger and host-meta actions to their own controllers

A request to `/test` would show the custom 404 page, but a request to
`/test.test` would return a 404 with an empty body.

This change ignores the format on incoming catch all route requests, so that the
html 404 page is returned on these requests.