Refactor SSEDownNotice to use hooks

[MichaelDeBoey]

What kind of change does this PR introduce?
I've extracted @Saeris' changes to SSEDownNotice out of #1925.

What is the current behavior?

• Use mobx-react
• Use inject HOC

What is the new behavior?

• Use mobx-react-lite
• Use new useStore hook

Checklist:

• Documentation N/A
• Tests
• Ready to be merged
• Added myself to contributors table N/A

[MichaelDeBoey]

@Saeris I think you should destructur store just like you did in the other files

Suggested change

	const store = useStore();
	const {
	editor: { currentSandbox: { template } },
	server: { status },
	} = useStore();