* Copy released JSON to board URL, not new one
Fixes#8180
The draft release generates a ZIP and JSON. Instead of rebuilding the ZIP
on the publish step (which may result in a different SHA256 due to file time
differences in the new ZIP), just copy the one from the published release
directly.
Also clean up and remove unneeded environment variables and CI steps.
* Be more paranoid about JSON format, check after d/l
Convert the continuous integration process to use GitHub's internal
CI cloud. Allows us to run up to 20 jobs in parallel, speeding up
CI immensely. Keep a short Travis-CI run, too, just for sanity and backup.
Uses new keys and secret when publishing a release to
esp8266.github.io.
