renamed sign in  module and added it to Rspec config file

Per your notes on this commit https://github.com/jpalmieri/blocitoff/commit/9b683a96ddf7f6221c1e83997d50aa21423429c5#commitcomment-8862903

`SignInHelper` and dropping the `capy_` prefix :+1:

Maybe a name like `sign_in` instead of `authenticated_user`? `authenticated_user` doesn't quite cover what's going on in the method.