Merge branch 'add-python39' into 'master'

Add Python 3.9 base image

See merge request common/dockerfiles!36

base/python:3.9

+FROM python:3.9.2
+ MAINTAINER Tamas Gal <tgal@km3net.de>
+
+ RUN apt-get update -qq && apt-get install -y -qq libhdf5-dev git
+
+ # LLVM 10
+ RUN echo "deb http://apt.llvm.org/buster/ llvm-toolchain-buster-10 main" > /etc/apt/sources.list.d/llvm10.list && \
+     wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add - && \
+     apt-get update -qq && apt-get install -y -qq llvm-10
+ ENV LLVM_CONFIG /usr/lib/llvm-10/bin/llvm-config
+
+ RUN pip install -U pip setuptools wheel
+
+ RUN pip install numpy
+ RUN pip install scipy pandas sklearn statsmodels numba numexpr tables h5py
+ RUN pip install pytest pytest-cov docopt sphinx sphinx-gallery
+ RUN pip install matplotlib seaborn pillow ipython jupyter notebook pillow