Fallback to gateway.ipfs.io

[dylanPowers]

When the local or custom gateway fails for any reason, fall back to gateway.ipfs.io.
Implementation details:

• Recheck every 5 minutes?
• Use /version api to check if up
• Have a command in the options menu to manually check and show the status

[jbenet]

• Recheck every 5 minutes?

FWIW, checking it the service is available locally on every page load is super cheap, because it's local (0 latency). Can start there and do something more complicated later.

• Use /version api to check if up

yep, this is a good use case for /version

• Have a command in the options menu to manually check and show the status

+1

[dylanPowers]

The resulting solution is to wait until a request failure occurs, flag that the local gateway is in a failure state, and then wait 30 seconds before attempting to send requests to the local gateway again. That ended up being the most reasonable solution.

I've closed this in commit 5327452