Code review comment for lp:~leonardr/lazr.restful/active-versions

This branch makes two major changes:

1. It introduces a new web service specifically for testing the multiversion code. This is pretty much a full copy of the WSGI test service, though I was able to import a few classes from the WSGI test service rather than re-defining them. (Many classes, even empty ones, had to be re-defined so that grok would handle them properly.)

Most of the multiversion tests in examples/base/tests/service.txt have been moved to examples/multiversion/tests/introduction.txt

2. It replaces the string service_version_uri_prefix (this is "beta" in the Launchpad web service) with a list of active_versions (this would be ["beta"] in the Launchpad web service). A request to any of the versions in active_versions will succeed, and although all versions still serve the exact same resources, the URLs to those resources will change depending on the version number.