feat(authInterceptor): ignore flag and cache auth

ignoreAuthorization:
Allow <code>$http.post(url, data, { ignoreAuthorization: true })</code> to ignore certain post requests (for servers that didn't allow Authorization in cors config)
cache auth:
maintain a reference to <code>auth</code> before injecting again
This should be an `||` otherwise I don't think it'd work as `$injector` will always have `auth`