[bulk-upload] dont die upon one failed XML import but continue on the next one
[bulk-upload] implement function in Ab4sToolkit to verfiy image
[bulk-upload] fix image download and update booking resources
 * handle incorrect image file (e.g. corrupted file)
 * more verbose logging
 * fix logic for checking downloading image file extension
 * fix skip image download when existing resource is not updated
[bulk-upload] remove unused variable