Add the User object and unit test.

This adds the User object, which is passed into every view. It
has `isAnonymous()`, `isAdvisor()`, and `isChair()` methods for
determining the user's type. This is useful for the RedirecView,
as well as enforcing the user is of a certain type to see certain
views.

Eventually we'll need methods to access the other fields of the
user, and we'll add them as we need them.