Specify ENV LANG=C.UTF8

Dockerfile_generator should generate sensible default Dockerfiles, so Anthony's recommendation has been included in the main template https://www.youtube.com/watch?v=SYwbEcNrcjI
This is set in the runner stage (the final one that can actually be used). This could be set in a shared common base stage instead (in which case build stages that want a different LANG would need to override it).

Linted and a sample of Dockerfiles (with all params set) built in CI.

v1.0.4 Python launcher.

Dropped jinja2-cli dependency