rdmorganiser/rdmo: 0.14

Fixes and new features: Switch to Python3, drop Python2 support Switch to Django2.2, drop support of older Django versions Note: From version 0.14 on RDMO will not work with Python2 anymore. With Django 2.1 the support of old MySQL and PostgresSQL versions was dropped. Please look into Django's release notes before you start your RDMO update to avoid surprises later during the update process Steps to upgrade: pip install --upgrade rdmo python manage.py collectistatic adjust RDMO app's config/urls.py to Django2 schemes, a working example can be found at https://github.com/rdmorganiser/rdmo-app/blob/master/config/urls.p