Added tests for sessions controller, question controller, and answer controller

Fixed sessions bug which was not adding user data to the session.
Fixed layout so that a logged-in user can log out.
Added tests to ensure the sessions controller redirects to the proper pages on successful login and unsuccessful login.
Added tests to ensure logged in users can ask questions.
Added tests, created answers controller, views and routes so logged in users can answer a question directly on question#show. 


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Notes:
Included suggestions for future testing inside of sessions_controller_spec.
To do: Link sign in page to site navigation.
Answers controller still needs to be fully implemented and tested