More rework of feed item list to deal with missing feeds.
Merge remote-tracking branch 'upstream/master'
More error handling improvements.  Added developer debug mode.
Merge remote-tracking branch 'upstream/master'
Adding preferences for offline story limit and image download concurrency.
Merge remote-tracking branch 'upstream/master'
Switch mark-unread task to use story hash.
Change save-story to use story hash.
Changed the read later success confirmation to use the checkmark HUD instead of an alert view.
In manual mark as read mode, clicking on a story *should* mark it as read.
Cleaning up text on preference for manual mark as read.
Fixing small text importer bug with missing encodings.
Adding media symlinks for ios.
Adding necessary exception handling to text view.
Adding missing folder feeds to USF.
Typo in missing feeds adder.
Merge branch 'master' into offline

* master:
  Typo in missing feeds adder.
  Adding missing folder feeds to USF.
  Adding necessary exception handling to text view.
  Adding media symlinks for ios.
  Fixing small text importer bug with missing encodings.
  Cleaning up text on preference for manual mark as read.
  In manual mark as read mode, clicking on a story *should* mark it as read.
  Further fixing context menu.
  Fixing right-click menu when opening with menu icon.
  Fixing hidden story indicator button on intelligence slide.
  Removing unneeded dependencies.
  Better title for contextmenu pref.
  Adding preference to use either native browser context menu or NewsBlur's context menu.
Merge branch 'offline'

* offline:
  Adding preferences for offline story limit and image download concurrency.
Trimming river URL by allowing 'f' to be used as a feed id parameter.
Fixing iOS crash on empty unread stories by providing correct data structure. Thanks to @linnet for spotting the bug.