Merge branch 'bug-10921-pass-renderingmanager-to-qmitkstdmultiwidget'

• bug-10921-pass-renderingmanager-to-qmitkstdmultiwidget: Default initialize all member variables. Forward declare mitk::RenderingManager. pass RenderingManager into QmitkStdMultiWidget and use throughout, or use Global RenderingManager - fix typo pass RenderingManager into QmitkStdMultiWidget and use throughout, or use Global RenderingManager