Migration for user model.
test user is_authenticated. --ch16l045--
user.is_authenticated always returns true. --ch16l045-1--
Add conditional login/logout things to nav bar. --ch16l047--
pass login url to client side js. --ch16l048--
helper wait_to_be_logged_in ornot fns. --ch16l050--
extend ft to check login persistence and logout. --ch16l049--
amend wait_for_element_with_id to show page text on fail. --ch16l052--
add logout url based on std django one. --ch16l053--
wire up logout button to url in template. --ch16l054--