Fall back to public gateway after trying local API

[hackergrrl]

If I run ipget <hash> I'd expect to (in order):

1. connect to the IPFS node running on my local machine
2. ask the public gateway via HTTPS

We could also try spawning an ephemeral node, but the gateway is already well-connected and should give a faster response. Lots of switches and flags for controlling this flow can come in after.

[hackergrrl]

We already spawn an ephemeral node, so let's stay with this for the time being. Using the public gateway would only let us fetch individual files -- right? -- which would mean many round trips for fetching directories.