MDL-47960 behat: fix my private files navigation

Caused by the my private files link being in user menu too..
MDL-47960 badges: behat failures caused by usermenu
MDL-47960 messages: behat failures caused by user menu
MDL-47960 behat: Fixed message node navigation

in i_send_message_to_user, we should use navigation node
step, as there might be multiple links with same name.
MDL-25057 mod_forum: Stop duplicating forum_read posts from cron

This also includes an upgrade script to delete the existing duplicates.