add ``localizer`` property to the request (refs #508)
remove duplicate of `Test_get_locale_name.test_name_on_request`
test the default localizer
test a custom localizer
remove test that explicitly sets a registry on the request

outside tests the router puts the registry on the request, but in tests it sometimes needs to exist as well.  however, it doesn't make sense to test something that's only done in tests anyway
don't use the default locale when testing custom localizer

also, use an object as a dummy localizer for better readability
clean up test names