* switch docker image to alpine base
* Docker: switch packaging image to alpine
* use alpine image for build containers
* switch base images in build script
* only try to set up phantomjs on x86_64, reduce number of layers
* phantomjs binary is bundled with grafana
* chore: mirror the Dockerhub readme
Seems like the dockerhub readme is out of sync with this one. Let's update this one to make them identical.
* chore: add changes part of 6.3.0-beta1 to the docker image README
* chore: add the date to the 6.3.0-beta1 changes in the CHANGELOG