We shall now use Go and Mage to manage the Flow services. The templates
have been converted to Go templates, Mage has replaced Make and the
helper bash scripts have been rewritten in Go.
- Change the instance name to 'Free Flow'.
- Change the local GTS docker image version from 'latest' to
$GTS_VERSION.
- Use GTS_DOCKER_IMAGE_DIGEST to specify the image digest.
- Allow users (i.e. myself) to upload custom CSS.
