Drop root privileges in container

Through this MR, the image does not run anymore as UID 0, which should improve (perceived) security and remove some nagging by i.e uWSGI.

To be tested:

• If it can be used with the current DB, (may need to chown it to 1000:1000, but please: backup first, test afterwards)

Dockerfile

@@ -5,6 +5,8 @@ WORKDIR /app
 EXPOSE 5000
 
 # First, copy and install only the requirements...
+RUN useradd -ms /bin/bash python
+USER python
 RUN pip install --upgrade pip setuptools
 RUN pip install pipenv
 COPY Pipfile.lock .