Mouse events handlers works for UB types and for some Qt types. Mouse events for other items hanlded by QGraphicsView.
It solves some troubles with items selections and fixes Sankore-721.

Fixed some related issues.

UBToolWidget.cpp/.h cleaned too.

Implemented Sankore-729 - previews images for web search results supports images, audios, videos and flash content.
Images previews is adjusted now.
Mime type detection mechanism is more common now.

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).

Frame buttons