title: Resizable container views containing view controllers
body: <p>I want to be able have several UIViewControllers on the screen at once, arranged as panes, as per the diagram below. 
  With the ability to:</p>
  
  <ul>
  <li>add additional panes while the program is running. </li>
  <li>drag the bars between the panes to resize them</li>
  </ul>
  
  <p>I was thinking of using container views (which are just view controllers?)</p>
  
  <p>How would I best achieve this?</p>
  
  <pre><code>        ┌───────────────────┳────────────────────────────┐
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          │                   ┣━━━━━━━━━━━━━━━━━━━━━━━━━━━━┫
          │                   ┃                            │
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          ┣━━━━━━━━━━━━━━━━━━━┫                            │
          │                   ┃                            │
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          └───────────────────┻────────────────────────────┘
  </code></pre>