Fix the block sign that was not removed correctly

Summary:
Remove the annotation and simply show / hide the overlay widget

Use a text overlay widget on top of the QmitkRenderWindow

A fixed warning message can be shown / hid using the public function.

Test Plan:
manual UI testing

• start MITK, open the segmentation plugin view, load different images
• create a segmentation node for one of the image
• activate a tool and try to draw on the render window
  • drawing should be possible but warning signs should appear
  • perhaps you have to perform a global reinit or reint to another node to see the warnings
• reinit to the reference geometry
  • drawing should be possible without warning signs
• also test 4D images, static / dynamic segmentation

Reviewers: floca, kislinsk, s434n, O1 MITK Reviewer Group I, O3 MITK Reviewer Group II

Reviewed By: floca, O1 MITK Reviewer Group I, O3 MITK Reviewer Group II

Subscribers: s434n, kislinsk, floca, kalali

Maniphest Tasks: T26376

Differential Revision: https://phabricator.mitk.org/D730