improve docker workflow

[tobybellwood]

This PR does a few things:

• It modifies the dockerfile build to use a multistage build - which almost halves the size of the resultant image
• It introduces a pair of docker images - one for a production build, and one for a development build. Only the production build is presented in Lagoon.
  -it makes a small change to the way tours are activated, and enables them on the development docker image