Reset mapper for crosshair plane nodes

Summary:
Reset mapper everytime the data is changed

This is required since SetData clears the previous list of mappers.

Remove unnecessary layer information

The PlaneGeometryDataMapper2D does not take the layer-information
into account.

Test Plan:
manual rendering test

1. open MITK, load an image
2. open the ImageCropper plugin
3. select the loaded image in the plugin
4. see how everything looks as expected
5. close the Standard Display, open the MxN Display
6. see how everything looks as expected
7. create a new bounding box
8. move the handles of the bounding box

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

Reviewed By: s434n, O3 MITK Reviewer Group II, O1 MITK Reviewer Group I

Subscribers: kalali, s434n

Maniphest Tasks: T29394

Differential Revision: https://phabricator.mitk.org/D759