Fix bug publish screenshot (#762)

[Preview this branch](https://cosmos-explorer-preview.azurewebsites.net/pull/762?feature.someFeatureFlagYouMightNeed=true)

The main change in this PR fixes the snapshot functionality in the Publish pane-related components. Because the code cell outputs are now rendered in their own iframes for security reasons, a single snapshot of the notebook is no longer possible: each cell output takes its own snapshot and the snapshots are collated on the main notebook snapshot.
- Move the snapshot functionality to notebook components: this removes the reference of the notebook DOM node that we must pass to the Publish pane via explorer.
- Add slice in the state and actions in notebook redux for notebook snapshot requests and result
- Add post robot message to take snapshots and receive results
- Add logic in `NotebookRenderer` to wait for all output snapshots done before taking the main one collating.
- Use `zustand` to share snapshot between Redux world and React world. This solves the issue of keeping the `PanelContainer` component generic, while being able to update its children (`PublishPanel` component) with the new snapshot.

Additional changes:
- Add `local()` in `@font-face` to check if font is already installed before downloading the font (must be done for Safari, but not Edge/Chrome)
- Add "Export output to image" menu item in notebook cell, since each cell output can take its own snapshot (which can be downloaded)
![image](https://user-images.githubusercontent.com/21954022/117454706-b5f16600-af46-11eb-8535-6bf99f3d9170.png)

package.json

@@ -56,6 +56,7 @@
     "datatables.net-dt": "1.10.19",
     "date-fns": "1.29.0",
     "dayjs": "1.8.19",
+    "dom-to-image": "2.6.0",
     "dotenv": "8.2.0",
     "eslint-plugin-jest": "23.13.2",
     "eslint-plugin-react": "7.20.0",
@@ -97,7 +98,8 @@
     "swr": "0.4.0",
     "terser-webpack-plugin": "3.1.0",
     "underscore": "1.9.1",
-    "utility-types": "3.10.0"
+    "utility-types": "3.10.0",
+    "zustand": "3.5.0"
   },
   "devDependencies": {
     "@babel/core": "7.9.0",
@@ -109,6 +111,7 @@
     "@types/codemirror": "0.0.56",
     "@types/crossroads": "0.0.30",
     "@types/d3": "5.9.2",
+    "@types/dom-to-image": "2.6.2",
     "@types/enzyme": "3.10.7",
     "@types/enzyme-adapter-react-16": "1.0.6",
     "@types/hasher": "0.0.31",