title: How to disable ion-fab button?
body: <p>I have fab-button as below and I want to disable it if form is not valid, but based on docs at <a href="http://ionicframework.com/docs/v2/api/components/fab/FabButton/" rel="nofollow noreferrer">http://ionicframework.com/docs/v2/api/components/fab/FabButton/</a> it seems fab-button doesn't have <code>disabled</code> property.</p>
  
  <pre><code>&lt;ion-fab right bottom [disabled]="!profileForm.valid"&gt;
      &lt;button ion-fab color="primary"&gt;&lt;ion-icon name="md-checkmark"&gt;&lt;/ion-icon&gt;&lt;/button&gt;
    &lt;/ion-fab&gt;
  </code></pre>