Create gateway and signalhubws instances under Dat domains.

[RangerMauve]

dat-js is currently making use of a gateway and signalhubws instance that I set up on a server I have lying around.

I'm totally OK with this setup, but I think that it would be better going forward if it was using instances that were under the datproject domain to make it more obvious to users what it is and where to go if it's down. (Also in case I get run over by a bus).

Steps to get this done:

• [ ] Register subdomains on datproject
• [ ] Set up a VM with the services
• [ ] Set up a letsencrypt certificate with auto-renewal (I did this with nginx)
• [ ] Update dat-js and docs to point to the new domains

cc: @karissa @joehand

[okdistribute]

@joehand was working on this