Simplified code for pinch event

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@24163 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
More continuous pinch zooming

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@24164 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e