title: How to add a class to a popover title
body: <p>I'm using the popover's bootstrap element but I don't know how to attribute to it a class. I'd like to create a customed background color for each different class.
  Here's my popover build (in javascript)</p>
  
  <pre><code>$(element).popover({
                      'placement': 'top',
                      'animation': true,
                      'html': true,
                      'title' : variable,
                      'content': html
                  });
  
                  $(element).popover('show');
  </code></pre>
  
  <p>If I do : </p>
  
  <pre><code>$(element).popover({
                      'placement': function(context, src) {
                          $(context).addClass($(src).data('customClassName'));
                          return 'top';},
                      'animation': true,
                      'html': true,
                      'title' :feature.get('features')[0].get('name') + ' (' +  feature.get('features')[0].get('type') + ')',
                      'content': html
                  });
                  $(element).popover().addClass('TESTCLASS');
                  $(element).popover('show');
  </code></pre>
  
  <p>The result given will be 
  <a href="https://i.stack.imgur.com/g1zDi.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/g1zDi.jpg" alt="enter image description here"></a></p>
  
  <p>As you can see the class is not in the same div that the popover-title</p>