Fix crosshair visibility
Summary:
Keep renderer-specific property of helper nodes
This is required so that crosshair data nodes are not globally
visible.
Test Plan:
manual testing
- open the MITK workbench, load an image
- close the StdDisplay, open the MxNDisplay
- change the synch-mode on top of a render window
- see how the crosshair stays visible, regardless
of the synch state
- compare with behavior without this diff
Reviewers: s434n, O3 MITK Reviewer Group II
Reviewed By: s434n, O3 MITK Reviewer Group II
Subscribers: kalali, s434n
Maniphest Tasks: T29403
Differential Revision: https://phabricator.mitk.org/D790