title: Xcode - if file is clicked, find existing tab instead of always opening new
body: <p>In Xcode 10.0, say I have two files open in two tabs, fileA.txt and fileB.txt. I have the tab with fileA active and focused. If I try to open fileB.txt <strong>from the navigator</strong>, I want it to switch to my existing tab that already has fileB open rather than opening fileB in the focused tab (and knocking out fileA).
  I believe this is the default behavior of Eclipse and Visual Studio.</p>
  
  <p>Bonus question: how can I make a <strong>single-click</strong> on a file in the navigator <strong>do nothing</strong>? Currently it opens the file (a behavior I only want when I double-click).</p>