refactoring (open / drag and drop files)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@23457 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
properties files and related resources automatically updated from ggbtrans

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@23458 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e