title: WPF listbox groupping by substrings
body: <p>My object has property that stores more strings separated by separator.
  I want to display list of such objects in WPF listbox with grouping enabled. What I need is to have groups according to substrings.</p>
  
  <p><em>Object1: Property = "string1;string2;string3"</em></p>
  
  <p><em>Object2: Property = "string2;string3"</em></p>
  
  <p>I expect listbox to be displayed like that:</p>
  
  <h2>string1</h2>
  
  <p>Object 1</p>
  
  <p>Object 2</p>
  
  <h2>string2</h2>
  
  <p>Object 1</p>
  
  <h2>string3</h2>
  
  <p>Object 1</p>
  
  <p>Object 2</p>
  
  <p>Is that possible? </p>
  
  <p>Thank you for your help.</p>