Move to GitHub Actions

[kinow]

These changes close #321

Requirements check-list

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• Does not need tests (why? build scripts only).
• No change log entry required (why? e.g. invisible to users).
• No documentation update required.

[kinow]

Draft as not sure if others will agree with the move - it would probably mean moving other projects to GitHub Actions too. Took me around 10 minutes to prepare the workflow in GitHub (I've seen people using actions, build, workflows, etc... the docs of github actions use workflows too), and another 30-40 minutes to test caching and write ticket and prepare the PR.

Shouldn't take long for cylc-uiserver and smaller projects. Probably will take a couple of days or a bit more for Cylc Flow due to functional tests. But it would allow us to use Docker containers and actions. Which, if faster on GitHub, would be a huge advantage (Docker containers can be slow to start up and provision/install required software depending on the infra).

[hjoliver]

I don't see any reason not to do this; let's make a decision in the meeting on Tuesday.

[kinow]

Ready for review.

[hjoliver]

👍 Looks like nice clean setup. I'll take your word that it works. I don't think we need a 2nd review for this.

[kinow]

Thanks @hjoliver !

Your merge here has triggered the first GitHub action :-)

https://github.com/cylc/cylc-ui/actions?query=workflow%3ACI

I have disabled the push-trigger in Travis for cylc/cylc-ui (those two options under the General text)

[kinow]

(first action took 3m57s, better than 7m30s from travis, but hope it will be even better now with the cache ready)