redesign of dock widgets title bar with configurable colors * octave-dock-widget.cc (constructor): connect settings_changed signal to new slot handle_settings; (handle_settings): common settings for all dock widgets: style sheet, this functions calls notice_settings for individual settings; (make_window,make_widget): change dock-/undock-icon * octave-dock-widget.h: new slot handle_settings * settings-dialog.cc (constructor): check box and color pickers for title bar; (write_changed_settings): store colors to settings file * settings-dialog.h: new color-pickers as class variables * settings-dialog.ui: check box and color pickers for title bar colors

gnulib-hg = gnulib-hg