Added icon preview in EditTextAnnotationDialog
REVIEW: 121490
Added icon preview in EditGroundOverlayDialog
REVIEW: 121491
Added row for icon in EditBookmarksDialog
REVIEW: 121485
Added icon preview in EditBookmarkDialog
REVIEW: 121492
Showing warning in case if user doesn't have avconv installed

REVIEW: 121488
BUG: 340467
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
cosmetics
attributes--
split matrices in texture vertex shader