title: reloadData() of UITableView with Dynamic cell heights causes jumpy scrolling
body: <p>I feel like this might be a common issue and was wondering if there was any common solution to it.</p>
  
  <p>Basically, my UITableView has dynamic cell heights for every cell. If I am not at the top of the UITableView and I <code>tableView.reloadData()</code>, scrolling up becomes jumpy. </p>
  
  <p>I believe this is due to the fact that because I reloaded data, as I'm scrolling up, the UITableView is recalculating the height for each cell coming into visibility. How do I mitigate that, or how do I only reloadData from a certain IndexPath to the end of the UITableView? </p>
  
  <p>Further, when I do manage to scroll all the way to the top, I can scroll back down and then up, no problem with no jumping. This is most likely because the UITableViewCell heights were already calculated.</p>