Node panics shouldn't bring down the editor

[Keavon]

Sandbox various components, like the node graph, in panic handlers. Reload those components instead of having to reload the whole page. Avoid making the document get lost since that's highly destructive to the user and almost always shouldn't be corrupted by whatever bug resulted in the crash, so the document data should most likely be in tact.

Some options:

• Move the graph evaluator into a web worker?
• Something with panic handlers?
• Reboot the node graph executor somehow?

[TrueDoctor]

@Keavon should we close this or remove it from the in progress tasks?

[Keavon]

Closed by #1846