Refactor (#862)

* Initial factoring out of parts of the LayerUI component

2360 → 2224 LOC

* Create a Section component

* Break up src/index.tsx

* Refactor actions to reduce duplication, fix CSS

Also consolidate icons

* Move scene/data.ts to its own directory

* Fix accidental reverts, banish further single-character variables

* ACTIVE_ELEM_COLOR → ACTIVE_ELEMENT_COLOR

* Further refactoring the icons file

* Log all errors

* Pointer Event polyfill to make the tests work

* add test hooks & fix tests

Co-authored-by: dwelle <luzar.david@gmail.com>

package-lock.json

@@ -10744,6 +10744,12 @@
         "sha.js": "^2.4.8"
       }
     },
+    "pepjs": {
+      "version": "0.5.2",
+      "resolved": "https://registry.npmjs.org/pepjs/-/pepjs-0.5.2.tgz",
+      "integrity": "sha512-acPfplXnTKaG8p7VBgkNaBJSGsZu7LYrqEmLCQFoeHYl21B74mMBeVoQA/Gl9u5GmysgzrOCeHsEjw0mXo61nw==",
+      "dev": true
+    },
     "performance-now": {
       "version": "2.1.0",
       "resolved": "https://registry.npmjs.org/performance-now/-/performance-now-2.1.0.tgz",