Listener pattern for GoogleDriveFileChooser

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@29671 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
More efficient redefinition when new definition is the same

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@29672 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e