MDL-44606 Assign: Some grading functions are missing sesskey protection
MDL-43877 blocks: Files from blocks in my/ were accessible to the world
MDL-43119 Add valid until dates for tokens created by login/token.php

3 months were decided

Conflicts:
	login/token.php
MDL-45126 do not allow guests see name and summary of hidden course
MDL-44750 Assign: Do not reveal student identities to screen readers
MDL-45332 repository_url: URL parameter is using PARAM_URL