Merge branch 'mj/pdf-errors' into 'master'

db/db.ddl

db/upgrade-20210126.sql

mo/db.py

mo/submit.py

mo/web/org_contest.py

mo/web/templates/base.html

mo/web/templates/org_contest_solutions.html

mo/web/templates/org_submit_list.html

mo/web/templates/parts/org_solution_table.html

mo/web/templates/user_contest.html

mo/web/templates/user_contest_task.html

mo/web/user.py

static/mo.css