refactor: polish

- Fix mis-used dependencies. Add the roughly proposed 'extends' model
  for notebook renderers. Keep it out of contribution schema for now
	until we can work it more.
- Made new loading work with JS modules.
- Consolidated the 'old style' code in the renderer so that we can just
  delete it when the time comes.
- Removed duplicated code and sharp edges from the 'queue' mechaism.

extensions/notebook-markdown-extensions/package.json

@@ -25,24 +25,18 @@
       {
         "id": "markdownItRenderer-katex",
         "displayName": "Markdown it katex renderer",
-        "entrypoint": "./notebook-out/katex.js",
-        "mimeTypes": [
-          "text/markdown"
-        ],
-        "dependencies": [
-          "markdownItRenderer"
-        ]
+        "entrypoint": {
+          "extends": "markdownItRenderer",
+          "path": "./notebook-out/katex.js"
+        }
       },
       {
         "id": "markdownItRenderer-emoji",
         "displayName": "Markdown it emoji renderer",
-        "entrypoint": "./notebook-out/emoji.js",
-        "mimeTypes": [
-          "text/markdown"
-        ],
-        "dependencies": [
-          "markdownItRenderer"
-        ]
+        "entrypoint": {
+          "extends": "markdownItRenderer",
+          "path": "./notebook-out/emoji.js"
+        }
       }
     ]
   },