title: Yii2.0 - Ajax form submit and dropdown update
body: <p>I have a model with a category relation. In my model form i have dropdown to choose from existing categories, and a modal popup for adding additional categories. But the modal submit reloads the page to insert and update.</p>
  
  <p>Now, id like the modal submit button to close the modal, submit the form trough ajax and update the dropdown field. </p>
  
  <p>I remember doing this in Yii 1.1, is there a neat way to do this in Yii2.0? Any pointers?</p>