Provide facility for configuring application-required middleware

[nyergler]

Some things, like CSRF protection (`#361 </issues/361>`_), benefit
from the ability to uniformly call helpers before and after a
request is processed by the view. In the case of CSRF, we want to
confirm that the token matches before processing the view, and make
sure the token is set before delivering the response. Unlike WSGI
middleware, this sort of wrapping is an integral part of the
application.

[nyergler]

This is implemented in 569-application-middleware in my clone
([https://gitorious.org/\ :sub:`nyergler/mediagoblin/nyerglers-mediagoblin/commits/569-application-middleware](https://gitorious.org/`\ nyergler/mediagoblin/nyerglers-mediagoblin/commits/569-application-middleware))

[Christopher Allan Webber]

Looks great to me. I suspect as for "configuration' of this
middleware our current config files suffice... maybe we could
create a standard for sections of the application for various
middleware configs, but otherwise looks great. Merged, and closed!

[Will Kahn-Greene]

The original url for this bug was ​http://bugs.foocorp.net/issues/569 .