Fix some bugs in MxN crosshairscorrectly enable/disable crosshairs and fix crosshair rendering on inverted geometries

Summary: This takes care of a couple of bugs we noticed in the crosshairs of the MxN view. Crosshairs were not enabled when loading a layout preset. Crosshairs (i.e. their related helper nodes) were not deleted correctly when reducing the amount of windows. Sometimes the crosshairs were not drawn correctly (one line drawn completely through) when shown on an image with an inverted dimension (e.g. axial view of brain.nrrd). This diff takes care of all those problems.

Test Plan: Close the Std view, open MxN view, load an image, change the number of windows manually and by loading a preset, and click around in the windows to see if the crosshair moves correctly. When showing helper nodes, reducing the amount of windows or closing the MxN view should delete any related helper objects.

Reviewers: O1 MITK Reviewer Group I, O3 MITK Reviewer Group II, kalali, floca

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

Differential Revision: https://phabricator.mitk.org/D787