migration to python3.6 and django 2.1

Status:
  it is possible to set up application (in the venv) create database: ./manage.py migrate
  and to start it ./manage.py runserver 0.0.0.0:8000
  Many incompatibility issues were fixed, however, there are many more.

TODO:
  gunicorn -> https://pypi.org/project/gunicorn/ shows systemd config, should be used
  celery -> doesn't work at all now
  tasks.py - commented out because of import error, it is related to celery
  registration - API must be studied, it was changed and there are some incompatibilities
  translation - setlan/ django.conf.urls.i18n - this was not tested, maybe it doesn't work
  old migrations - all migration files were moved into backup; new initial
	migrations were created (because old ones import south which is not supported
	any more); the current migrations are missing default values such as protocols,
	thenactions, ...