Uploading a large file - inform about progress consistently

[kosarko]

When uploading large files, it eventually shows Processing uploaded file(s)... (it's now safe to close this page). If you really do leave the page; and then come back; the file might not be shown among uploaded files (depends on timing, how much processing it needs to do and how quickly you come back) and no other information is shown about a "in progress" upload. It seems that waiting in the submission form won't show the file...you have to refresh/leave & come back at some point to see the file