dgml: unused properties
GeoPainter: don't draw polygons twice
fix TileId::fromCoordinates() and according test case

Fix test case by taking into account that third parameter of GeoDataCoordinates c'tor is altitude, not the unit.
Fixing the test case forces consistent usage of GeoDataCoordinates::Degree in TileId::fromCoordinates().
introduce MarbleView
introduce MarbleGLView
introcude GlLayerInterface
clear depth buffer between layer rendering
TextureLayer
PlacemarkLayer
introduce triangulation algorithm for polygons

* taken from http://www.crystalspace3d.org/svnroot/crystal/CS/trunk/{include/csgeom/triangulate.h, libs/csgeom/triangulate.cpp}.
GeometryLayer
introduce GeoGraphicsScene::GlTile and use glDrawElements
adapt PlacemarkLayout
use shaders
GLRenderer