9.1.1 Edit form
9.1.2 Unsuccessful edits
9.1.3 Testing unsuccessful edits
9.1.4 Successful edits (with TDD)
9.2.1 Requiring logged-in users
9.2.2 Requiring the right user
9.2.3 Friendly forwarding
Add users index for displaying all users.
9.3.1 Users index, 9.3.2 Sample users, 9.3.3 Pagination, 9.3.4 Users index test
9.3.5 Partial refactoring, 9.4.1 Administrative users, 9.4.2 The destroy action, 9.4.3 User destroy tests