Run github.io from master instead of gh-pages

[timbl]

I note the FIXME in

https://github.com/solid/solid-ui/edit/master/Documentation/developers/publish_README.md

Why not switch github.io to run from master instead of gh-pages?

[angelo-v]

We would need to check-in the built files into master and mix it with the sources. I prefer keeping it in the gh-pages branch and automate the process as proposed in the readme. Will remove the storybook build from my PR as well.