introduce WidgetMoverButton (to realize the "move layer" feature in the upcoming layer oriented sample editor)

introduce sample selection list (model & view) - the left pane of the new layer oriented sample editor

move item infos to item catalog (in the future the info will be used at different locations, not only the sample toolbox)

move example infos to example factory (in the future the info will be used at different locations, not only the sample toolbox)

lambda-connections couldn't be automatically disconnected when deleting ScriptPanel

this reduces name2registry in GUIExamplesFactory to a triviality