Changed Icon Sizes so Buttons dont' use as much space.
Added missing include files. Compiles with current Slicer head.
Merge pull request #2 from gsi-biomotion/STD

SquaredDifference - new CLI module
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
Merge branch 'master' into STD

Conflicts:
	RegistrationQualityModule/Logic/vtkMRMLRegistrationQualityNode.h
	RegistrationQualityModule/Resources/UI/qSlicerRegistrationQualityModule.ui