Add Sessions controller and first tests
Pass simple session tests
Test for signin failure
Test for signin success
Add signin form
Add Users.create method for signing in
Test for problematic flash persistence
Pass flash persistence test
Include Sessions helper
Test for remember_token
Update database to support remember_token
Test for blank remember_token
Create remember token and pass test
Add Sessions helper signin
Add current_user method
Add signed_in? helper method; Add account menu
Test that newly signed up user is signed in; Pass test
Test for successful sign out
Add and use sign_out helper method