Zip import/export (based from zip-import-export branch)

[jsoules]

This is a modification of @magland's zip-import-export branch (PR #53) to use the amended data model from PR #77.
UI features are unchanged from that PR, so I'll refer to that for description, and this write-up will focus on the code changes (particularly as distinct from that PR/branch).

Most of the changes are to back-end files located under the gui/src/app/SPAnalysis directory. Front-end changes are under gui/src/app/pages/HomePage/. A few other smaller changes are in other directories and I'll describe them with full paths.

--
Probably the biggest focus of this PR is to establish standardized filesystem representations for the parts of the overall data model (SPAnalysisDataModel). This mapping is mainly implemented in FileMapping.ts. I've also created a new file for serialization code in SPAnalysisSerialization.ts. The reducer also had some significant changes to handle some new ways of updating the data model.

On the front-end side, code is mostly the same as in @magland's branch. I made some small changes to the ExportWindow.tsx and ImportWindow.tsx components to move some of their logic into the back-end code section (incl. the reducer), but as this is conceived as an update to that branch I tried to leave most of the functionality untouched.

Additionally, I've added replaceSpaces.ts and triggerDownload.ts functions in the util directory; these are small and straightforward.

Here are some notes on the back-end changes:

• FileMapping.ts: Probably the trickiest part, but is commented pretty extensively.
  • Defines an enum for filesystem filenames (e.g. main.stan, data.json, etc.)
  • Defines a mapping from filenames to data-model field names.
  • Defines a type that maps filenames to filename contents.
  • Function to map a data model to a (partial) list of persistent files.
  • Function to take a (partial) list of persistent files and map their contents to a data model.
• SPAnalysisReducer:
  • Add a new action type that takes a partial list of data model fields & maps their contents to an instance of the data model.
  • Added functions to update data model metadata, data model sampling opts, and other fields (the "files" fields, which are text blobs).
  • All above functions have an option to determine whether or not to preserve any existing data that isn't being touched.
• SPAnalysisSerialization: New file.
  • Move the "serialize everything to local storage" functions (which had been in the data model file).
  • Moved the zip serialization/deserialization code here from where it was in PR frontend: import/export #53 (on the UI components).
• SPAnalysisDataModel:
  • Added type exports, including one for the data model with the "ephemera" key omitted.
  • Added utility functions for copying permanent state to the ephemera, for returning appropriately stringified fields from the data model object, for looking up defined-field keys, and tracking whether models have been changed.
• SPAnalysisContextProvider: trivial changes.

[WardBrian]

A few misc comments/questions

[magland]

Tried in a codespace and cot this error

 [ERROR] No matching export in "src/app/util/replaceSpaces.ts" for import "replaceSpaces"

    src/app/SPAnalysis/SPAnalysisSerialization.ts:2:9:
      2 │ import { replaceSpaces } from "../util/replaceSpaces"
        ╵          ~~~~~~~~~~~~~


    at failureErrorWithLog (/workspaces/stan-playground/gui/node_modules/esbuild/lib/main.js:1472:15)
    at /workspaces/stan-playground/gui/node_modules/esbuild/lib/main.js:945:25
    at runOnEndCallbacks (/workspaces/stan-playground/gui/node_modules/esbuild/lib/main.js:1315:45)
    at buildResponseToResult (/workspaces/stan-playground/gui/node_modules/esbuild/lib/main.js:943:7)
    at /workspaces/stan-playground/gui/node_modules/esbuild/lib/main.js:955:9
    at new Promise (<anonymous>)
    at requestCallbacks.on-end (/workspaces/stan-playground/gui/node_modules/esbuild/lib/main.js:954:54)
    at handleRequest (/workspaces/stan-playground/gui/node_modules/esbuild/lib/main.js:647:17)
    at handleIncomingPacket (/workspaces/stan-playground/gui/node_modules/esbuild/lib/main.js:672:7)
    at Socket.readFromStdout (/workspaces/stan-playground/gui/node_modules/esbuild/lib/main.js:600:7)

I think there was a function name change?

[jsoules]

Tried in a codespace and got this error
[...]
I think there was a function name change?

Yep, I committed the change direct from the comment and missed that it needed to be corrected where it is imported as well. Should be fixed now.

[WardBrian]

This looks good to me! I left a couple comments, none of which are blockers on a merge IMO

[WardBrian]

Happy to leave this until after merge, just echoing my discussion from #53 that I think uploading a single file should keep the drop box enabled to allow you to also add a second/third etc