Merge branch 'offline'

* offline:
  Moving from image_url -> image_urls in iOS app as well.
  Mark read up/down icons.
  image_url -> image_urls
  Fixing progress in image caching.
  Fixing crash when missing cached image.
  Reading cached images and using in stories. A single iamge is nowhere near enough. Need a refactor to account for all images.
  Fixing image cache notifier message for date of last download.
  Caching images for offline. Progress bar works, but the message is wrong.
  Fixing loading indicators blue-ness.
  Setting the stage for caching images. Just need the cache writer and cache reader.
  Refactoring order and read_filter. Global preferences!
  Adding new preferences modal.
  Handling edge case of reading a story on the web, syncing with ios, then reading in ios offline should mark the story as read through syncing, overriding offline cache.
  Correct notifications for offline and on.
  Full offline. Adding feeds table and caching of feed list by username. Also optimizing unread story fetching by placing all db calls in a background thread.
Handling validation for image urls.
Fixing progress bar for cached images.
Speeding up unread story hashes.
Fixing scroll on story for traversal buttons in those in between story heights.
Moving ios and android from media to clients.
Adding symlinks from old media/clients to clients/
Preparing ios 2.4 for distribution.