Map Reconstruction Support for JSON Files from Legacy Mapknitter

[segun-codes]

Fixes #1350

Make sure these boxes are checked before your pull request (PR) is ready to be reviewed and merged. Thanks!

• [X] PR is descriptively titled 📑 and links the original issue above 🔗
• [ ] tests pass -- look for a green checkbox ✔️ a few minutes after opening your PR -- or run tests locally with grunt test
• [X] code is in uniquely-named feature branch and has no merge conflicts 📁
• [X] screenshots/GIFs are attached 📎 in case of UI updates
• [X] @mention the original creator of the issue in a comment below for help or for a review

Hi @jywarren, having spent some time unsuccessfully trying to get programmatic download URL for the JSON files for legacy Mapknitter from wayback machine, I decided to implement the DnD aspect first before returning to the said URL-based map reconstruction shortly. Here, the DnD aspect is ready for your review. Your thoughts?

Illustration 1: ceres-2

Illustration 2: 01-test--2

Illustration 2.1: Illustration 2 above updated into this after some more seconds

Illustration 3: --10

Illustration 4: -emf

Illustration 5: I tried out the URL from error messages returned to browser and got this

[jywarren]

Ah sorry, DnD = drag n drop, sorry now I feel silly! 😂

[segun-codes]

This is looking good -- I didn't get what DnD meant but you mean like downloaded and dragged onto the page, instead of directly from the URL, right? That's OK!

Yes.

[segun-codes]

Code is now updated, you may want to take a second look. Thanks!

[jywarren]

Noting for future readers, we're doing a follow-up for correct corner order in https://github.com/publiclab/Leaflet.DistortableImage/pull/1359