minor Dockerfile updates and rename

Docker/shellb3-cspp-py38.Dockerfile → Docker/Dockerfile

-# docker build --build-arg BORT=develop . -f shellb3-cspp-py38.Dockerfile -t shellb3-cspp-py38:latest
-# docker run -e SHELLB3_ARCHIVE_DIR=/dock -it --rm -v $HOME/dock:/dock -w /opt/shellb3-cspp-py38/ShellB3 shellb3-cspp-py38 /bin/bash -l -c "unset LANG; bash shallbethree.sh bin_dist"
+# docker build --build-arg BORT=dev --build-arg TRIM=cspp --build-arg PYTHON_VERSION=38 . -f Dockerfile -t shellb3-dev-cspp-py38:latest
+# docker run -e SHELLB3_ARCHIVE_DIR=/dock -it --rm -v $HOME/dock:/dock -w /opt/shellb3-cspp-py38/ShellB3 shellb3-dev-cspp-py38 /bin/bash -l -c "unset LANG; bash shallbethree.sh bin_dist"
 FROM centos:7
 RUN yum -y install gcc-gfortran gcc-c++ unzip perl patch byacc bison flex glibc-devel.i686 glibc-devel.x86_64 xz epel-release wget make bzip2 xz automake autoconf m4 which
 RUN yum -y install git git-lfs 
 RUN test -d /opt || mkdir /opt
 RUN test -d /work || mkdir /work
-ARG BORT
+ARG BORT=main
 ARG TRIM=cspp
 RUN cd /opt && echo "using branch or tag ${BORT}" \
  && git clone https://gitlab.ssec.wisc.edu/rayg/ShellB3.git --branch ${BORT} --single-branch --depth 1 shellb3-cspp-py38