Subdirectory mounting

I'd like to use Clockwork Raven alongside other admin capabilities. This requires it not conflicting with those routes, so I added a the ability to mount the whole thing into a subdirectory.

    def self.mounted_path
      "/turk"  # empty for root, "/dir_name" for mounted
    end

Tests pass in both cases. At least the same as they were before.

I switched the tests over to use the routes helpers, which I'm not a huge fan of, but it beat adding this mounted notion all over the place.