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-lock.json

@@ -5255,6 +5255,12 @@
         "@types/d3-selection": "*"
       }
     },
+    "@types/dom-to-image": {
+      "version": "2.6.2",
+      "resolved": "https://registry.npmjs.org/@types/dom-to-image/-/dom-to-image-2.6.2.tgz",
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+      "dev": true
+    },
     "@types/dom4": {
       "version": "2.0.1",
       "resolved": "https://registry.npmjs.org/@types/dom4/-/dom4-2.0.1.tgz",
@@ -9667,6 +9673,11 @@
         }
       }
     },
+    "dom-to-image": {
+      "version": "2.6.0",
+      "resolved": "https://registry.npmjs.org/dom-to-image/-/dom-to-image-2.6.0.tgz",
+      "integrity": "sha1-ilA2CAiMh7HCL5A0rgMuGJiVWGc="
+    },
     "dom-walk": {
       "version": "0.1.2",
       "resolved": "https://registry.npmjs.org/dom-walk/-/dom-walk-0.1.2.tgz",
@@ -25918,6 +25929,11 @@
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       "resolved": "https://registry.npmjs.org/zalgo-promise/-/zalgo-promise-1.0.46.tgz",
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+    },
+    "zustand": {
+      "version": "3.5.0",
+      "resolved": "https://registry.npmjs.org/zustand/-/zustand-3.5.0.tgz",
+      "integrity": "sha512-fwZfax2c954pWB+RYXHXG0HWyuoUj8YiNykRjZC/w6L7ay9fPQ7M90mgDVP1KJsRqxLsDILBWSNxuzw5BkCpxA=="
     }
   }
 }