Load and Store sketches

[nilclass]

Currently the sketch is cleared when refreshing the page. It's not possible to export them anywhere (except by loading a single sketch onto the board and getting it back from there later).

Let's allow at least:

• Saving the current sketch to a text file
• Loading a sketch from a text file

[Architeuthis-Flux]

So, on the Jumperless itself, it does save the list of bridges in that simple [1-2,3-4] format on the filesystem. But now that we have control of net colors and stuff, maybe I should also save the last netlist in the machine readable format too.

But yeah for storing more than one file it should be on the computer.

Just a thought that doesn't really apply here, I really like how Falstad circuit simulator deals with this, it looks like they just base64 the whole setup and pass that in the url.

But also this will be run locally so we could just save the response to ::getnets in a txt file with headers for each one with names and stuff. Which is probably better because they'll be human readable.

[nilclass]

I like how falstad does it, but using a link does not really work when stuff runs locally, since the port may vary, or the user may be on a different machine than where jumperlab is served from.

For now I added the ability to save to a file (like a download, similar to falstad's "export to text") and load from a file again (the user needs to select it, like a file upload).

The data saved is the entire netlist as JSON, so the same format that jlctl uses internally (which should be more or less the same that's accepted by ::netlist).