worked on centering of images and display of additional panels in data viewer

modules/gui/src/data_viewer/argand.cc

modules/gui/src/data_viewer/argand.hh

modules/gui/src/data_viewer/data_viewer.cc

modules/gui/src/data_viewer/graphics_image_item.cc

modules/gui/src/data_viewer/graphics_image_values_item.cc

modules/gui/src/data_viewer/viewer_panel.cc

modules/gui/src/data_viewer/viewer_panel.hh

modules/gui/src/data_viewer/widget_layer_item.cc