title: UICollectionReusableView for section header not working
body: <p>I created a UICollectionReusuable view for UICollecton view section header. I use the following code the implement the header view.</p>
  
  <pre><code>- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath {
  ThemeHeader *headerView = [[ThemeHeader alloc] init];
  headerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader
                                                                   withReuseIdentifier:@"header"
                                                                          forIndexPath:indexPath];
  NSString *title = @"Title for the header";
  headerView.title.text = title;
  return headerView;
  </code></pre>
  
  <p>}</p>
  
  <p>It crashes giving me the following error:</p>
  
  <p>-[UICollectionReusableView title]: unrecognized selector sent to instance 0xac846a0'</p>
  
  <p>My ThemeHeader class looks like this</p>
  
  <pre><code>@interface ThemeHeader : UICollectionReusableView
  @property (strong, nonatomic) IBOutlet UILabel *title;
  
  @end
  </code></pre>
  
  <p>I appreciate your help in advance.</p>