Adding preferences for offline story limit and image download concurrency.
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.