Merge branch 'data_viewer' of git@bc2-dng01.bc2.unibas.ch:/opt/git/GIT_DATA/ost into data_viewer

Conflicts:
	modules/gui/src/data_viewer/data_viewer.cc
	modules/gui/src/data_viewer/data_viewer.hh
	modules/gui/src/data_viewer/graphics_image_item.cc
	modules/gui/src/data_viewer/graphics_image_item.hh
	modules/gui/src/data_viewer/viewer_panel.hh