Update to 2.8.3

Upstream changes:
Moodle-2.8.3
Highlights
MDL-47935 - Atto Autosave message no longer covers text you are editing
MDL-44560 - Pagination in glossary category works correctly when entries have multiple categories
MDL-47792 - Course and Activity Completion Reports display vertical text without truncating
Functional changes
MDL-43386 - Lesson grade essay responses preserve HTML formatting
MDL-14730 - Allow linking to pages inside a lesson
MDL-47761 - Explanation is given to the users why they are unable to enrol in the course
MDL-47871 - Event monitor: Teacher can duplicate System rule
UI changes
MDL-44907 - Better styling of admin setting validation messages in bootstrapbase
MDL-48596 - Lesson editing page has correct layout used by other editing pages and does not obstruct page with blocks
MDL-47166 - Atto: outdent button is shown first followed by indent button
Security issues
A number of security related issues were resolved. Details of these issues will be released after a period of approximately one week to allow system administrators to safely update to the latest version.

Fixes and improvements
MDL-48765 - Improved icon alignment on course enrolment methods page
MDL-40285 - When assignment is submitted by one team member it is shown as submitted for all team members
MDL-38142 - User forum posts page no longer displays error for the hidden course
MDL-36877 - Final lesson page is displayed when course setting "Show gradebook to students" is set to "No"
MDL-48073 - Group filter is preserved when moving to next page of enrolled users
MDL-40326 - Course reset also resets lesson progress bar
MDL-48383 - Cron no longer warns about disabled enrol_imsenterprise after each scheduled task
MDL-48914 - Roles assignment page does not display user select if there are too many users preventing from php memory error

(wen)