title: add a search bar to header in collection view with custom flow layout
body: <p>I am trying to add a search bar as the header to a custom flow layout class. </p>
  
  <p>I know how to add it in storyboard if the flow layout is not custom by simply checking the section header box, but as soon as i use a custom class, that option is no longer available.</p>
  
  <p>Mostly I am having trouble conceptualizing layout attributes and how to implement them. 
  Also I'm not sure if I should be putting methods in my <em>datasource</em>, <em>view controller</em>, or flow <em>layout subclass</em>, so please be specific about those. </p>
  
  <p>The tutorial on Ray Wenderlich only shows the storyboard method.</p>