Use label pixel value in segmentation preview tool
Summary:
Add specific segmentation pixel value for thresholding
In order to generate the correct output image the threshold filter
of both the FastMarching-tool and the Threshold-tool need to know the
pixel value of the active label.
Storing the current active label pixel value can be done inside the
common base class.
Test Plan:
manual testing
Perform the steps in T28986 (and T28131)
Reviewers: floca, kislinsk, O1 MITK Reviewer Group I
Reviewed By: floca, O1 MITK Reviewer Group I
Subscribers: kalali, kislinsk, floca
Maniphest Tasks: T28986, T28131
Differential Revision: https://phabricator.mitk.org/D597