title: ios: Queue blocks in background and execute when network becomes available
body: <p>I am developing an app using parse.com API (hosted backend which provides API to save data on their servers). I want to be able to use the app seamlessly online and offline. 
  For this I would need to use a queue where I can place blocks that require network access. When network does become available, the blocks should be executed serially and when the network goes offline, then the queue processing should be suspended.</p>
  
  <p>I was thinking of using GCD with suspend/resume as the network becomes available/unavailable.
  I was wondering if there are any better options? Will this work if the app is put in the background? Case in point here is that a user saves some data when the network is unavailable (which gets queued) and then puts the app in the background. Now when the network becomes available, is it possible to do the saving in the background automagically?</p>