Improve rendering of GPX tracks and routes.

The rendering of tracks and routes is now identical to the rendering
of tracks and routes created by Marble itself, except that the color
is slightly more saturated in order to make it possible to distinguish
them.

BUG: 311210
REVIEW: 110161
remove declaration of unimplemented method
make TextureMapperInterface::setRepaintNeeded() non-virtual

* avoids duplicate code
add const version of MarbleModel::treeModel()
require the more specific GeoScene{Texture/Vector}Tile when loading textures/vectors respectively
remove unused attribute
remove unused parameter
remove VectorTileMapper::initTileRangeCoords()
respect level zero layout from .dgml file

* fixes maximum tile calculation for given level
* makes vectorosm theme work again
no need to inherit from TextureMapperInterface
Fix endless loop for constant elevation profiles

yPos++ < ... does not terminate when operating on +-inf
remove unused attribute
remove unused methods
remove unused parameter
remove redundant slot
leave invisible vector tiles in cache for better performance
use TileId as key for documents in cache
document are implicitly removed from GeoDataTree by CacheDocument
split polygon when tessellated points are hidden

BUG: 315922
REVIEW: 110195
remove redundant statement which slipped in in commit 640caff71989569d4688a3ae9af056ae42cbc367