Users signup and signin

[Trello card - Users can signup](https://trello.com/c/5InGLM8W/10-as-a-guest-i-can-sign-in)
[Trello card - Users can signin](https://trello.com/c/bSXGdzE0/9-as-a-guest-i-can-sign-up-for-an-account-with-my-email)