Add this changes to make components specs clear
The `sign_in(nil)` method was a bit hard to understand IMHO. After all, in controller and system tests we don't have to specify no user is signed in; that's the default behavior. So we're making it the default behavior for component tests as well.
We're choosing `sign_in` instead of `login_as` because IMHO component tests are more similar to controller tests than they are to system tests.
