title: Using constants in Interface Builder
body: <p>In my projects I typically use a constants file with values like <code>GUTTER</code> and <code>PADDING</code>to keep spacing in my UI consistent throughout.</p>
  
  <p>I've started getting into Interface Builder and would like a way of using constants to space my elements instead of hard coding values.</p>
  
  <p>So I was wondering if there is a way to set config values for my project that IB could read, whether they're environment vars or in a property list or whatever?</p>