Add devicelink to whitelist.

Issue #270.
Drop KegbotSite.is_active and SiteActiveMiddleware.
Update whitelisted paths.
stats: Store user ID instead of username.

Issue #271.
Add custom staff_member_required decorator.

Also adds django auth login template.
Add "rename_user" command (for power users only for now).

Issue #271.
api: Create/delete tap support; add more tests.
stats: Insulate against malformed UID.
v0.9.29