Remove huxley.advisors app from the codebase.

This scraps the entire huxley.advisors app. It also removes other
code relevant to it, like the account-type template tags, the
default_path context processor, and the EnforceUserTypeMiddleware.

Test Plan: Run test suite (remove the default_path test), and
make sure logging in via www still works.

Resolves #205.
Would we want to add a generic redirect url here?