Make it easier to have more than one instance attached to domain

[burdakovd]

Why this would be useful:

1. Run more than one instance, for higher redundancy, easier scalability, and better latency due to instance in local region being available
2. Easier to provision new machine to prod withotu downtime

What needs to be changed/checked:

1. nano-dns to forward DNS request to all peers, to answer acme-challenge correctly
2. Route 53 to do have multiple IP addresses and filter out unavailable ones with health check, and returning remaining addresses (possibly chosen by proximity to viewer)
3. Audit page to understand those new Route 53 rules
4. Travis to deploy to multiple hosts (likely works already)