T29329 Fixed 4D problem. Tool uses now the right time step.

Summary:
+ Fixed T29329
+ Added UX improvment: Preview label have now same name and color like the seed lables.

Test Plan: Code review, manual testing of grow cut -> error in T29329 cannot be reproduced

Reviewers: O1 MITK Reviewer Group I, kislinsk

Reviewed By: O1 MITK Reviewer Group I, kislinsk

Subscribers: s434n, kislinsk

Maniphest Tasks: T29329

Differential Revision: https://phabricator.mitk.org/D739