Intersect quadric part / plane makes a conic section

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@35986 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Use settings for plane visibility

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@35987 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e