asdk header node workaround

header.swift

func tableView(tableView: UITableView!, viewForHeaderInSection section: Int, delegate : PollHeaderNodeDelegate?) -> UIView! {
        var view = tableView.dequeueReusableHeaderFooterViewWithIdentifier("Header") as? UITableViewHeaderFooterView
        
        if view == nil {
            view = UITableViewHeaderFooterView(reuseIdentifier: "Header")
        }
        
        view?.backgroundView = UIImageView()
        
        let contentView = view!.contentView
        contentView.backgroundColor = UIColor.clearColor()
        if let vm  = self.sectionedDS.data?[section] {
            contentView.tag = vm.id.hashValue
        } else {
            contentView.tag = -1
        }
        
        for subview in contentView.subviews {
            subview.removeFromSuperview()
        }
        
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)) {
            [weak self] in
            
            var header = self?.tableView(tableView, loadNodeForHeaderInSection: section)
            
            if let pollHeaderNode = header as? PollHeaderNode {
                pollHeaderNode.delegate = delegate
            }
            
            var size = header?.measure(CGSizeMake(CGRectGetWidth(tableView.bounds), CGFloat.max))
            header!.frame = CGRectMake(0, 0, size!.width, size!.height)
            
            dispatch_async(dispatch_get_main_queue()) {
                if let pollHeaderNode = header as? PollHeaderNode {
                    if contentView.tag == pollHeaderNode.pollViewModel.id.hashValue {
                        contentView.addSubnode(header)
                    }
                }
            }
        }
        
        return view
    }