Fixed a bug - grouped items cannot be dragged by itself now.

"+" and "-" buttons does nothing if text item is empty.

Now text size in TextItem is the same on separate platforms.

SANKORE-477 	Erasing an object with the keyboard

- locked items is not editable now.
- toolbar for text item hides when item is locked

Fixed behavior of toolbar:
toolbar of media items hides after 5s of idle.

Fixed restoring of cursors at mouse release event on board.

It's icon is temporary.

Behavior implemented:
1. Can interact with all items without showing items frames (but ToolBar shows).
2. Cannot move items, but can drag images.
3. Selected items appears deselected when Play tool chosen.
4. Play tool don't requires selecting of item before interacts.
5. Cursor looks like tool icon in text and image widgets (should be the same in any others widgets, but now in w3c is not).

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

Locked items cannot be moved horizontally by its frame.

Text items can be resized correctly now.

PDF : Sankore overwrite Pdf layer to empty, after picture(shape) was "set as background"

Frame buttons

Text object :auto adjust of object works with fewest letters

Fix to Sankore 636. Now copyes of video and audio items stops in the sate tomes when stops original items.

Generating of missing thumbnails no more crashes Sankore.

Improved performance of navigating between pages.