[API Change] remove drawLine() and regionFromLine() from GeoPainter

* both were unused convenience methods in GeoPainter
* drawPolyline() and regionFromPolyline() can be used as replacements
[API Change] remove unused GeoPainter::drawPoints()

this method
* didn't provide any speedup improvement compared to calling GeoPainter::drawPoint() multiple times
* had a C-style API
wip idis
const'ify
remove ViewportParams parameter from MarbleGraphicsItem::paintEvent()
GeoGraphicsScene
const'ify changeViewport()
wip remove ScreenOverlayGraphicsItem from GeometryLayer
split LayerInterface::render() into paint() and setViewport()

* TODO: rename render() to setViewport()
const'ify GeoGraphicsItem::paint()