title: Ban / unban users using devise
body: <p>I know I can make an user <code>approved</code> or not <code>approved</code> using <code>devise</code>, therefor an user won't be able to log in until an admin approves them.</p>
  
  <p>I want an admin to be able to ban / unban users as well, which is different from approving since approving is an one way and one time process and I don't want to mix it up with banning. I sought out this functionality at devise's web site and didn't find anything valuable.</p>
  
  <p>Is there any devise's way to do that? </p>