Interactive SICP JS: should make use of folder mode in chapter 4 and 5

[martin-henz]

It would be nice to organize the programs in SICP JS chapter 4 and 5 into folders, using the new folder mode of Source Academy. For that, we'd need to look at the URL encoding:

sicp/javascript/processingFunctions/processSnippetJson.js

Line 216 in 269071f

const compressed = lzString.compressToEncodedURIComponent(

[martin-henz]

We would need to design an XML format for multi-file snippets.