Add missing changes for Planning?Measurement plugin - vector map display zoom

1) Add changes to the MapVectorLayer to implement vector map display
zoom
2) Minor clean up of PlanningLayer and PlanningPlugin class code
3) Fine tune map ruler re-sizing for display mode in MapCOntrolsLayer
Reset display zoom when Planning/Measurement plugin is disabled after being installed

Reset the display zoom  factor to 1 so that screen display will be the
same as if the plugin had not been installed.