Dockerfile update (#644)
Dockerfile update (#644)

- Updated images with newer versions, except for Node: the js stuff will not compile with a version > 10
- Removed python3-dev and sqlite3 in step 2, they are not needed
- Added flask to pip, cf. issue #621
- Some small improvements here and there like a good practice for gunicorn use in Docker cf. https://pythonspeed.com/articles/gunicorn-in-docker/
jelmer/isso,jelmer/isso,posativ/isso,posativ/isso,jelmer/isso,jelmer/isso,posativ/isso,posativ/isso