Roi results (rebased onto develop)



This is the same as gh-2650 but rebased onto develop.

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Problem noticed by @will-moore  while preparing material for workshop
The results tab was not populated until you select a ROI.

To test:
 * Draw few shapes on an image. Save.
 * Close the measurement tool and the viewer.
 * Re-open the viewer and the measurement tool.
 * Check that the Manage tab and the Results tab are populated.