Touch: allow file saving again

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@28354 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
More robust file saving (for case the included image file has no extension)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@28355 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Allow opening file without pictures after file with pictures was opened

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@28356 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e