title: Ext JS - Sencha cmd app configuration files and theme
body: <p>I'm using Ext JS and Sencha CMD and want to experiment with a few themes.</p>
  
  <p>Also I have read that the theme for an app can be changed in <code>app.js</code>(using theme property) and <code>sencha.cfg</code>(using app.theme property) and then run sencha app build.</p>
  
  <p>I would like to know,
  Why are this configurations in two different files?
  And Which is the correct way of doing this?</p>