title: Firebase, query "not equal to"
body: <p>Here my database structure :</p>
  
  <pre><code>{
    "feeling" : {
      "fake0" : {
        "fake1" : {...},
        "fake2" : {...}
      }
    },
    "profile" : {
      "fake0" : {...},
      "fake1" : {...},
      "fake2" : {...},
      "fake3" : {...}
    }
  }
  </code></pre>
  
  <p>If the logged user is "fake0", how can he fetch all profiles that are not in his feeling ?</p>
  
  <p>I would like to do something like :
  <code>ref("/profile", {notEqualTo: ["fake1","fake2"]}).on('once', .....)</code></p>
  
  <p>Perhaps my structure is bad, just tell me a better one and I will change it :) !</p>