This reverts commit 4aa0ee61.

When the time comes to merge dev into master (for real), the
following may be useful:
https://metlos.wordpress.com/2012/01/13/
git-merging-after-a-revert/

Simply added copying of zValue to the deep copy functions. As tested on
OSX, this does pose any problems when duplicating an item on-page (i.e
generating a new item with a zValue equal to its original).

persistence of not required media on disk. Second step updated the cleanSource methods in classes that handle files on disk

Navigation palette: thumbnails isn't refeshed after application added to the page

Fixed some related issues.

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.).