Merge branch 'jirka/messages' into 'devel'

constraints.txt

db/db.ddl

db/upgrade-20210322.sql

mo/db.py

mo/web/__init__.py

mo/web/org_round.py

mo/web/templates/org_round.html

mo/web/templates/org_round_messages.html

mo/web/templates/parts/messages.html

mo/web/templates/parts/user_news.html

mo/web/templates/user_contest.html

mo/web/templates/user_contest_task.html

mo/web/user.py

setup.py

static/js/news-reloader.js

static/mo.css