title: Using UIAppearance and switching themes
body: <p>I'm looking to theme my iOS app and have been reading up on UIAppearance. I want the user to be able to switch between a number of different visual themes from within the app. Changing a theme would then be shown in the UI.</p>
  
  <p>I'm thinking I could have a theme file that is a singleton loaded within the appDelegate.m. But after that i'm a little stuck on how this could be implemented?</p>