strudel.json editor

[felixroos]

with #621 , samples can now be loaded from disk.
The strudel.json file will be created automatically from the folder structure (if it does not exist).

To customize the samples, for example to create pitch zones, the strudel.json must be edited by hand.
It would be handy if the desktop app provided a way to edit the strudel json to reflect what is possible with samples (https://strudel.tidalcycles.org/learn/samples)