title: Add blinking to button
body: <p>I would like to draw a user's attention to a submit button anytime a radio button is selected and I would like to know if there's anyway to implement this in flutter. I have looked at the RaisedButton docs but there doesn't seem to be any property that flashes or shakes the button. The code below for instance initially has no radio button selected so the button is grayed out, once a choice is made amongst multiple radio buttons, the submit RaisedButton onPressed property value is no longer null but replaced with the action required; however I also want a situation where if a different radio button is selected, there is some way to add some motion (flashing/shaking button) to the submit button but not change the onPressed property</p>
  
  <pre><code>new Radio&lt;int&gt;(
  value: 1, 
  groupValue: 0, 
  onChanged: handleRadioValue
  )
  
  new RaisedButton(
  child: const Text('SUBMIT')
  onPressed: selected
  )
  
  handleRadioValue(){
  selected = groupValue == 0 ? null : submitButton();
  //change Raised button to attract attention}
  </code></pre>