title: Cannot import name 'input_function' from 'chatterbot.utils'
body: <p>I'm trying to implement feedback for bot replies created with chatterbot</p>
  <p><a href="https://github.com/gunthercox/ChatterBot/issues/935#issuecomment-324230394" rel="nofollow noreferrer">https://github.com/gunthercox/ChatterBot/issues/935#issuecomment-324230394</a>
  But it returns me 2 errors</p>
  <p>The first:</p>
  <pre><code>ImportError: cannot import name 'input_function' from 'chatterbot.utils' (/Users/xxx/Documents/.../utils.py)
  </code></pre>
  <p>The second one when I set the <code>DEFAULT_SESSION_ID = bot.default_session.id</code>:</p>
  <pre><code>Unresolved attribute reference 'default_session' for class 'ChatBot'
  </code></pre>