title: UITableView Section Header not showing
body: <p>I'm trying to make section headers with autolayout.
  A simple header with a title and a counter</p>
  
  <pre><code>class ProfilePeopleListHeaderViewCell: UIView {
  
    let titleLeftOffset = 12
    let counterRightOffset = 5
    let counterWidth = 50
  
    var title = "title" {
      didSet {
        titleLabel.text = title
      }
    }
    var numberOfPeople = 0 {
      didSet {
        peopleCounter.text = "\(numberOfPeople)"
      }
    }
  
    let titleLabel = UILabel()
    let peopleCounter = UILabel()
  
  
    convenience init(title: String, numberOfPeople:Int) {
      self.init()
      self.title = title
      self.numberOfPeople = numberOfPeople
      backgroundColor = UIColor.greenColor()
      titleLabel.textColor = Constants.Colors.ThemeGreen
      titleLabel.textAlignment = .Left
      if #available(iOS 8.2, *) {
        titleLabel.font = Constants.Fonts.Profile.PeopleListHeaderFont
        peopleCounter.font = Constants.Fonts.Profile.PeopleListHeaderFont
      } else {
        titleLabel.font = UIFont.systemFontOfSize(14)
        peopleCounter.font = UIFont.systemFontOfSize(14)
      }
  
      peopleCounter.textAlignment = .Right
      peopleCounter.textColor = Constants.Colors.ThemeDarkGray
  
      addSubview(titleLabel)
      addSubview(peopleCounter)
      self.titleLabel.snp_makeConstraints { (make) -&gt; Void in
        make.centerY.equalTo(self)
        make.height.equalTo(self)
        make.width.equalTo(peopleCounter).multipliedBy(3)
        make.left.equalTo(self).offset(titleLeftOffset)
      }
  
      self.peopleCounter.snp_makeConstraints { (make) -&gt; Void in
        make.centerY.equalTo(self)
        make.height.equalTo(self)
        make.width.equalTo(counterWidth)
        make.left.equalTo(titleLabel.snp_right)
        make.right.equalTo(self).offset(counterRightOffset)
      }
    }
  
  }
  </code></pre>
  
  <p>The code to retrieve the header is:</p>
  
  <pre><code>  let mutualFriendsSectionView = ProfilePeopleListHeaderViewCell(title: Strings.Title.MutualFriends, numberOfPeople: 0)
  
    override func tableView(tableView: UITableView, viewForHeaderInSection section: Int) -&gt; UIView? {
       if section == 1 {
          //mutualFriendsSectionView.layoutSubviews()
          return mutualFriendsSectionView
        }
    }
  
  override func tableView(tableView: UITableView, heightForHeaderInSection section: Int) -&gt; CGFloat {
      return 40
      }
  </code></pre>
  
  <p>I get a green background in the section header.
  But I don't see any label...</p>