Add an emergency shutdown state to notify people that the app is offline

[parrot9design]

@BennyOptions' latest forum post reminded me that, in the event of an emergency shutdown, we should trigger a banner message in the app so that people are aware most transactions will fail.

Governance functionality is still available after the shutdown. Is anything else affected?

[parrot9design]

Balanced is temporarily offline. Until operations resume, you can only claim rewards and participate in governance. Visit Discord for the latest updates.