Import PDF: progress bar is not visible

Now coping creates a full copy of already created item. Copy has it's own content (like video, audio or folder) and stores original item properties (like locked, pos, size, freezed e.t.c.).

The old code has to be removed and remaining bugs fixed.

Fixed pages shuffling.
Fixed refreshing thumbnail of new added page.
Some code refactoring and optimizations.

Frame buttons

Document explorer(navigator): pages of a document can not be moved using D'n'D