title: Check if ARSession is running (ARKit)
body: <p>I have an ARSCNView that can occasionally pause its <code>session</code> depending on the situation. Is there a way to check if its <code>session</code> is running?</p>
  
  <p>Something like this:</p>
  
  <pre><code>class myARView: ARSCNView {
      ...
      func foo() {
  
          if(session.running) {
              // do stuff
          }
      }
      ...
  }
  </code></pre>