Big image view

Fix issues related to big images viewing.
 * https://trac.openmicroscopy.org.uk/ome/ticket/10478
 * https://trac.openmicroscopy.org.uk/ome/ticket/10479

To Test:
* Open a big image
* Go to the bird eye view. click outside the red rectangle. This should change the selection
* Move the red rectangle to change selection, the move should be easier.
* Change selection using the scrollbar (main window)