Connect online/offline events to "document" as well as "window" to make it work with Cordova

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@35703 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
4.9.310.0

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@35704 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e