title: ngTagsInput - Set onTagAdding callback
body: <p>I'm trying to set a default function for the <code>onTagAdding</code> callback using the <code>tagsInputConfig</code> provider. No success.</p>
  
  <pre><code>tagsInputConfig.setDefaults('tagsInput', {
      placeholder: 'Search',
      maxTags: 10,
      minLength: 5,
      maxLength: 40,
      replaceSpacesWithDashes: false,
      onTagAdding: function (x,y,z) {
          debugger; // breakpoint is never called
      }
  });
  </code></pre>
  
  <p>All the other default options are set correctly, except for the callBacks. In the other hand, it works when I configure it as a property: </p>
  
  <pre><code>&lt;tags-input on-tag-adding="onTagAdding($tag)" ng-model="search"&gt;&lt;/tags-input&gt;
  </code></pre>
  
  <p>Is there any way to set a default function for this callback?</p>