Since I really want to use our existing infrastructure to model that we can
recognize something as a request handler without it having a route, we need this
as a separate concept. All tests have been adjusted.
The early modeling was based on flask, where all request-handling is based on
handling requests from a specific route. But with the standard library handling
and handlers without routes, the naming had to change.
BUT, since MyCustomViewBaseClass.post (django-v2-v3/testapp/views.py) and
Foo.post (django-v2-v3/routing_test.py) aren't handled, this raises important
question about how to do MRO without points-to :S
Added it to the `testapp` so it's easy to run the server to SEE that it works.
Added it to `routing_test` so it's obvious this is supported by our modeling
when we _know_ it's running Django 2/3.
