Move docker cli calls from webrob to separate daemon

Currently the webrob container needs access to the /var/run/docker.sock to create, run and stop user containers. This was achieved by creating a docker user group with ID 999 inside the container, adding the unprivileged ros user to that group and mount binding the /var/run/docker.sock.
If the docker user group on the host has a group ID other than 999, it will fail.

With this PR, a new docker container "dockerbridge" is introduced, it has access to the hosts /var/run/docker.sock file and runs as root. A python JSON-RPC server listens on port 5001 and provides the methods start_container and stop_container (moved from knowrob_docker.py). The webrob container only has access to the JSON-RPC port 5001 and will call it in knowrob_docker.py, no direct docker cli calls remain.