Move from Electron to Chrome Headless

[andymsuk]

Summary

Electron is currently used as the browser environment for running the standard tests. Electron has several quirks and currently is the cause of us having to maintain a Docker image for running bbc-a11y on certain environments.

I propose moving away from Electron and using Chrome Headless instead.

[EmmaJP]

Andy, assigning this to you temporarily, for investigation into what this change would actually involve in terms of work.

[andymsuk]

Have not written/changed any code yet, but from looking at the code and from remembering chats with @joshski, it should just be a case of working ./bin/bbc-a11y.js and all the stuff in electron folder to use Chrome instead of Electron.
Once again, it's not a quick task.

[oluoluoxenfree]

So far investigating options, we seem to have a choice between puppeteer, chrome remote launcher and chrome launcher.