Merge test

Dockerfile

 FROM python:3.8
 
 RUN apt-get update && apt-get install -y \
+    # requirements for OpenCV
+    libgl1-mesa-dev \
     # requirements to build python-ldap
     build-essential python3-dev libldap2-dev libsasl2-dev \
     && rm -rf /var/lib/apt/lists/*