Use node 16.x

It required converting mocha tests code into async since [@wdio/sync is
deprecated](https://webdriver.io/docs/sync-vs-async/) starting with
node v16.
It removed the dependency on fibers and on [node-gyp + python](https://
webdriver.io/docs/sync-vs-async/#common-issues-in-sync-mode) indirectly
though which is a great thing.

Also moved away from node-sass to sass since [node-sass is deprecated]
(https://sass-lang.com/blog/libsass-is-deprecated).

package.json

@@ -31,6 +31,7 @@
     "@mapbox/mapbox-gl-style-spec": "^13.15.0",
     "@mdi/react": "^1.4.0",
     "array-move": "^2.2.1",
+    "caniuse-lite": "^1.0.30001325",
     "classnames": "^2.2.6",
     "codemirror": "^5.52.0",
     "color": "^3.1.2",
@@ -66,6 +67,7 @@
     "react-motion": "^0.5.2",
     "react-sortable-hoc": "^1.11.0",
     "reconnecting-websocket": "^4.4.0",
+    "sass": "^1.49.9",
     "slugify": "^1.4.5",
     "string-hash": "^1.1.3",
     "url": "^0.11.0"
@@ -135,7 +137,6 @@
     "@wdio/mocha-framework": "^6.1.14",
     "@wdio/selenium-standalone-service": "^6.1.14",
     "@wdio/spec-reporter": "^6.1.14",
-    "@wdio/sync": "^6.1.14",
     "babel-eslint": "^10.0.3",
     "babel-loader": "^8.1.0",
     "babel-plugin-istanbul": "^6.0.0",
@@ -155,7 +156,6 @@
     "istanbul-lib-coverage": "^3.0.0",
     "mkdirp": "^1.0.4",
     "mocha": "^7.1.2",
-    "node-sass": "^4.14.1",
     "react-hot-loader": "^4.12.19",
     "sass-loader": "^8.0.2",
     "selenium-standalone": "^6.17.0",