ENH: Upgraded StackedLayerModel to desynchronize current and reference layers; (Mv2) Split main tool-bar into main- and render-toolbars; (Mv2) Added reference-layer combo box to tool-bar.

ENH: Implemented LayerStackItemModel (index+name) data query and signals; Improved StackedLayerModel signals to match QAbstractItemModel/LayerStackItemModel behavior.

ENH: Connected StackedLayerModel to LayerStackItemModel; Started implementing LayerStackItemModel; Improved StackedLayerModel.

ENH: Connected Raise/Lower layer; Implemented rotate up/down in layer-stack; Set main-window title with selected image basename.

ENH: Implemented Select next/previous layer in StackedLayerModel and connected it to/from image-view manipulator (keypress events only), renderer, widget.

COMP: Fixed compilation error on Windows platform due to use of std::pair(first, second) constructor initialization.

ENH: Separated ImageViewRenderer::UpdateScene() part from ::SetLayerStack() part; Removed old commented code.