title: Show all whitespace errors using Airline
body: <p>I'm using <em>Vim</em> with <em>Airline</em> plugin and whitespace extension and it shows me <code>mixed-indent</code> or <code>trailing-whitespace</code> errors in the bottom right corner. 
  <a href="https://i.stack.imgur.com/SQKAW.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/SQKAW.png" alt="enter image description here"></a><br>
  But there's only one (first) error with the line number there. I'd like to check all line numbers with errors like it is possible to check <em>Syntastic</em> errors using <code>:Errors</code> command. 
  <a href="https://i.stack.imgur.com/Gzvaym.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Gzvaym.png" alt="enter image description here"></a><br>
  Is there any way to do it ? Or the only solution is to correct the error and than go to the next one when <em>Airline</em> updates its status ?</p>