Have our BodhiBase.__json__ method take an optional 'request' argument

This will allow us to pass any bodhi model up to the Pyramid json renderer and
have it get serialized accordingly.
Explicitly use Pyramid's json renderer, instead of Cornice's simplejson one.

This will allow us to return our model instances directly from our views, so we
don't have to call __json__ ourselves everywhere and deal with JSON in our
templates
Return Update model instances from our services to our renderers.

As long as we use Pyramid's json renderer, they will get serialized
appropriately. This also let's us deal with the model objects in our templates,
as opposed to JSON.
Interact with our Update instances in our templates, instead of JSON.
Update our *2html helpers to deal with our DeclEnum instances
Have our @updates.get service accept json requests