extend json and npz export

[j042]

• extend json export to support multipatches
• support spline_data export
• support show_options export

[jzwar]

Yes, that sounds like a good extension. Also HiWi-able?

[clemens-fricke]

Show options are now in #358 for the json ex- and import. Should we also add it to npz? What about spline data, is that still an issue?

[j042]

having it in npz export and spline data support would be great