Merge branch 'remove-openpyxl' into 'master'

Remove openpyxl and jdcal dependencies

Closes #475

See merge request !1001

base/requirements.txt

@@ -5,6 +5,5 @@ elasticsearch==6.2.0
 hiredis==1.1.0
 ijson==2.3
 lxml==4.2.3
-openpyxl==2.4.9
 psycopg2-binary==2.8.6
 Twisted==19.7.0

requirements.txt

@@ -17,7 +17,6 @@ djangorestframework==3.11.1
 elasticsearch-dsl>=6.0.0,<7.0.0
 gitpython==3.0.8
 idna==2.10
-jdcal==1.3
 python-gitlab==1.7.0
 python-memcached==1.59
 pytz>=2018.7