Disable interpolation area when segmentation node is hidden

Summary:
Show interpolator only if valid data was selected

This was done on top of T28142, so that it can easily be integrated
in the refactoring of the segmentation plugin views.

Test Plan: manual workbench / UI inspection

Reviewers: kislinsk, O1 MITK Reviewer Group I, s434n

Reviewed By: kislinsk, O1 MITK Reviewer Group I, s434n

Subscribers: s434n, kalali

Maniphest Tasks: T28829

Differential Revision: https://phabricator.mitk.org/D604