CAS cell selection improvement

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@23485 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Debugging

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@23486 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e