Changes in Widget & Logic
1. Changed falsecolor from button to checkbox. It's now possible to go back to gray values, if falsecolorcheckbox is unchecked.
2. Added imagedifference logic, which is empty for now. Will implement Square Difference there.
Merging two different branches, because of some issues between them.
Merge branch 'master' of https://github.com/gsi-biomotion/slicer-dirqa