Exercise 9.6.7: Learn about the request object by inserting some of the methods listed in the Rails API into the site layout

Change-Id: I3e878d56e94241cf3d2e6ff62e32bf1ef636ed1e
Exercise 9.6.8: Write a test to make sure that the friendly forwarding only forwards to the given URL the first time. On subsequent signin attempts, the forwarding URL should revert to the default.

Change-Id: Id63e696da832f117f681adc54f9a9695a1a6921a
Exercise 9.6.9: Modify the destroy action to prevent admin users from destroying themselves

Change-Id: I5556c7273ff9946ed0c6263e37f0140a0a45de9a