ticket:250 added logging to errors that happen when adding files to cart
ticket:249 added is_task_done utility function
ticket:249 reworked mechanism that determine files loaded or not
Merge branch 't249_add_to_cart_never_completes'
ticket:250 fixed conflicts after merging
ticket:250 logging for cart add view
ticket:250 remove timestamp from matadata/manifest/summary filenames
Merge branch 't250_some_errors_lost'