Refactor KoImageData and KoImageCollection

This fixes the following:
* copy of shapes with a pattern backgound run into an assert
* make copy and paste of images and objects with pattern background work
* fix bug in WMFImportParser to use the image collection correctly. the image collection was not found
* make it possible to add also remote images e.g. over fish://
* make copy and paste of pages with background images work in kpresenter and kivio

Also done
* make sure that if the same picture is added more then once to use the same data for it
* added first unit tests for KoImageCollection
* use the shape saving context to store the images which need to go into the saved store.
* don't stop loading if e.g. a image can not be loaded.

I hope I did not break anything. As far as I can see all works well.
The karbon filters should be tested to see if it is all working as expected.
I also disabled the code in the shapeselector to show the clipboard as it crashes as soon you twice copy a picture.