Outdated Docker Images

[ghost]

I have issued several PRs to update or remove outdated Docker images. But some are left, that would benefit from some care:

• dhcp and snmpsimulator
  Both were created in 2016 by Julien and got very few updates since then. Both were not used by any appliance. They are currently commented out in the docker/docker_images configuration file and are therefore not built by the docker build system. With some care both could be nice applications.
• jupyter:v2 and jupyter27:v2
  Both depend on the outdated python versions, 3.7.7 and 2.7. So jupyter:v2 needs an update to a supported python3 version and jupyter27:v2 should probably be deleted.

As I'm not really interested in those images, someone else should take care of them.