title: Swift - How to dismiss all of view controllers to go back to root
body: <p>I want a my app can go to a first view controller when every time users want it.</p>
  
  <p>So I want to create a function to dismiss all the view controllers, regardless of whether it is pushed in navigation controllers or presented modally or opened anything methods.</p>
  
  <p>I tried various ways, but I failed to dismiss all the view controllers certainly.
  Is there an easy way?</p>