WIP: application tour when the user selects a feed for the first time.
UserConfigsController#update now accepts being sent the show_feed_tour flag.
FactoryGirl factory for User instances sets all "show tour" flags to false.

In most cases we want the user to be a returning user who has already completed all tours. In those cases where the behavior of a new user is being tested, this will be indicated explicitly.
Added acceptance tests for the feed tour.