GGBAPI: removed dead code, made sure getBase64 does not include thumbnail by default and that version which allows thumbnail is exported

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25132 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Fixed JSNI signature for getBase64

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25133 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e