WIP: new Dockerfile_v5.12.0

[rjleveque]

Based on old Dockerfiles. Seems to work ok, but need to update, add more packages, and PETSc if possible.

This worked....

docker build -t clawpack/v5.12.0_dockerimage -f Dockerfile_v5.12.0 ./

docker run -i -t -p 8889:8889 --name clawpack-v5.12.0_container \
      docker.io/clawpack/v5.12.0_dockerimage