change ImageProvider to interface; fix some typos
extract IImageProvider to common code;
extract base class of ImageDownloader
Merge branch 'unstable' into image-loading-refactoring

* unstable:
  …and on iOS
  add MapObjects property to DralloDetailsController
  reverse chunk of debug code
  adding map objects on Android
  replaced challengeEninge
  fixed last compile error. App is running on my phone again
  fix all compile time errors except two that are related to assembly versioning
  Fix some of compile errors
  added new challengeEngine with final map-features
extract even more code to base class
make ImageDownloadCallbackSet private
initialise image downloader inside
remove unused vars, add warnings for future removal
remove image loader lib from android
Revert "remove image loader lib from android"

This reverts commit 02e19fbeba5c69e704f28e54ea5515afc5121786.
Merge branch 'image-loading-refactoring' into unstable

* image-loading-refactoring:
  Revert "remove image loader lib from android"
  remove image loader lib from android
  remove unused vars, add warnings for future removal
  initialise image downloader inside
  make ImageDownloadCallbackSet private
  extract even more code to base class
  extract IImageProvider to common code; extract base class of ImageDownloader
  change ImageProvider to interface; fix some typos