Restore lxml requirement in base image for arkindex_common

Dockerfile

-FROM registry.gitlab.com/arkindex/backend/base:django-3.1 as build
+FROM registry.gitlab.com/arkindex/backend/base:django-3.1-lxml as build
 
 RUN mkdir build
 ADD . build
 RUN cd build && python3 setup.py sdist
 
-FROM registry.gitlab.com/arkindex/backend/base:django-3.1
+FROM registry.gitlab.com/arkindex/backend/base:django-3.1-lxml
 
 ARG COMMON_BRANCH=master
 ARG COMMON_ID=9855787

Dockerfile.binary

@@ -57,7 +57,7 @@ RUN python -m nuitka \
       arkindex/manage.py
 
 # Start over from a clean setup
-FROM registry.gitlab.com/arkindex/backend/base:django-3.1 as build
+FROM registry.gitlab.com/arkindex/backend/base:django-3.1-lxml as build
 
 # Import files from compilation
 RUN mkdir /usr/share/arkindex

base/requirements.txt

@@ -4,6 +4,7 @@ Django==3.1
 elasticsearch==6.2.0
 hiredis==1.0.0
 ijson==2.3
+lxml==4.2.3
 openpyxl==2.4.9
 psycopg2==2.8.5
 python-Levenshtein==0.12.0