Selection develop (rebased onto dev_5_0)



This is the same as gh-2554 but rebased onto dev_5_0.

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Fix https://trac.openmicroscopy.org.uk/ome/ticket/12264

To test:
 * expand a dataset with many images in tree in Insight
 * select all of the images in the dataset (in tree or in central pane)
 * with all the images still highlighted, click onto the dataset itself
 * the highlighting of the images should be remove