title: Bootstrap tagsinput Add item issue
body: <p>So, i started today using this bootstrap-tagsinput, first thing i tryied was adding a new tag dinamically, i spent now about an hour to do this simple task and i still have the same problem.
  Heres the code i'm using:</p>
  
  <pre><code>$("#test").tagsinput({
      allowDuplicates: true,
      itemValue: function(item) { return item._id; },
      itemText: function(item) { return item.name; }
  });
  
  $("#test").tagsinput('add', {_id: 1, name: 'Testing'});
  </code></pre>
  
  <p>The result i get is: <strong>Uncaught Can't add objects when itemValue option is not set</strong>
  but as you can see i do set itemValue. I also put the code in a <a href="http://jsfiddle.net/7fp5hh2j/2/" rel="nofollow">JSFiddle file</a> to be easy for you to test. I noticed not only itemValue is not being set but none of my options, because i also can't duplicate tags (but i allow it on options).</p>
  
  <p>Anybody know what is happening?</p>