Support FormWizard without the base view

[dcramer]

A common paradigm we're using while refactoring Sentry is inheriting from various base View classes. This is specifically to enforce authorization and acls. FormWizard provides a lot of nice behaviors, but it requires you to inherit from Django's CBVs. It'd be nice if FormWizard was a helper that wasn't bound to View behavior. Generally all of the generic Django CBVs have this issue, but FormWizard is a bit more trivial to adapt to than TemplateView.

[dcramer]

(just to prevent anyone from suggesting it, mix-in's and any other complex OO behavior are not a solution to this problem)