(iOS image downloader) make more methods private
(iOS image downloader) add method for cancelling the callback
fixed wrong access to dictionary
don’t use imagesdownloader for local images
handle case when downloading same url again
cleanup
clear image of reused cell
add images; use new arrow images in fullscreen image slider
Merge branch 'DA-353-android' into unstable

* DA-353-android:
  add images; use new arrow images in fullscreen image slider
  clear image of reused cell
  cleanup
  handle case when downloading same url again
  don’t use imagesdownloader for local images
  fixed wrong access to dictionary
  (iOS image downloader) add method for cancelling the callback
  (iOS image downloader) make more methods private
adapt android code + rename IsSpecialUrl method