Access website obj directly under resources.get

I'm trying to get rid of request.website, so that instead we just pass
in the website object where ever we need it. In simplate contexts,
website is available as a global. It's unpythonic ("one right way") and
overcomplicated to have it also available at request.website.
Remove request.website from our bundled simplates

We have website already in simplate contexts.
Remove request.website from aspen.io
Remove request.website from dispatcher

Pass in website object instead.
Remove request.website entirely
Merge pull request #385 from gratipay/media_type_default

remove request.website