Trying to solve the remaining media support problems

- apply Coolo's patch for resolving media:/ URLs (from #93569)
- close CameraUI cleanly
- ask user if he wants to cancel the current operation when closing
- cancel operation when closing
- delete object when closed
- dont add new tasks to the queue when closing
- Allow only once CameraUI per CameraType object
- store current UI with a QGuardedPtr
- when a non-closed UI is found up and running, raise it, dont create a new one
- when camera interface is called via DCOP (probably from media menu)
- call KWin::deIconifyWindow
- call KWin::activateWindow()
- do not compute image dimension when listing from a UMSCamera. This is a _huge_
speedup, say 5 minutes to 5 seconds.
- do only compute image dimension if requested in UMSCamera
- compute image dimension if not yet done in CameraItemPropertiesTab
- various speed and crash fixes in CameraUI/CameraIconView
- do not crash when the first item was deleted from camera and then removed from IconView
- do not request exif for items which will be deleted
- IconView: allow to delay updating frequency a bit
- use a ched itemRect for CameraIconView. Its faster, but more importantly,
there was a crash with a pretty long story

BUGS: 126112
CCBUGS: 127846, 93569