feat: rewritten Figure shortcode supporting multi-resolutions

New shortcode supports
- enable re-usable *optimized* image assets from new primary media library location at `assets/images/`
- new behavior: load image from page dir falling back to media library at `assets/images/` and then to remote URI.
- multi-res support. leading to increased perf.
- custom ID for cross-refs
- efficient, vanilla (non-jQuery), MIT licensed image zooming
- FancyBox now only loaded for Gallery shortcode
- themeable SVG support
- native lazy loading

Experimental, may change.

BREAKING CHANGE:
Move any figure images (i.e. not the `sharing.*` image) from `static/media/` to `assets/images/`

See #2164

package.json

@@ -15,7 +15,8 @@
   "main": "index.js",
   "dependencies": {
     "bootstrap": "^4.4.1",
-    "instant.page": "^5.1.0"
+    "instant.page": "^5.1.0",
+    "medium-zoom": "^1.0.6"
   },
   "devDependencies": {
     "eslint": "^7.17.0",