determine notation for labels just once
remove unneeded method call

The method call immediately returns here since there's no dialog yet.
Allow for labels in GeoLineStringGraphicsItem.
GraticulePlugin: Use GeoGraphicsItems for rendering the grid
factor out ScreenLayer from GeometryLayer
wip idis
GeoGraphicsScene
always create a canvas image in texture mappers
GeoPainter::mapTexture()
const'ify
remove ViewportParams parameter from MarbleGraphicsItem::paintEvent()
const'ify changeViewport()
const'ify GeoGraphicsItem::paint()
remove customPaint()
WIP: split LayerInterface::render() into paint() and setViewport()
deactivate to-be-ported RenderPlugins