title: Dynamically add fields to fieldGroup
body: <p>I have created this <a href="http://jsbin.com/cexezaneni/edit?html,js,output" rel="nofollow">jsbin</a> in which I have a <code>fieldGroup</code> with 2 fields. There is a button called <code>AddRow</code> that upon pushing, I am trying to dynamically add another field to the <code>fieldGroup</code>.</p>
  
  <p>Is this possible with Formly? This example is a simiplied version of how it will work within my solution. I will be getting a list of various field types that I need from a Rest call. Whatever is returned from this call will be the fields that need added into the <code>fieldGroup</code>. Starting small... I am just trying to add a field based off of a button click.</p>