Clean the code, little optimisation

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@31860 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
* triangulation : check if polygon is convex
* drawing convex polygon
* set dummy texture

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@31861 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Use triangulation to draw polygons

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@31862 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e