MDL-46531 editor_atto: Color plugins should use classes rather than hardcoded colours
MDL-47777 assign: max files hard coded to setting

The current file submission is hard coded to a maximum of 20 files
possible.  While the user can choose a number less than 20, the maximum
is still set in code.  This converts the hard coded 20 to a site setting
defaulting to 20.
MDL-36874 mod_book: Add uarrow() output renderer.

In preparation for Book navigation improvements in MDL-36874, this commit
adds a uarrow() output renderer, to complement rarrow() and larrow().
MDL-36874 mod_book: Add text navigation.

Based on a patch by Matthew Cannings, this replaces Book's previous/next arrow
image links with a choice of: no links, image links, or chapter title text links.
MDL-47975 assign: Stop gap fix for random time fails.
MDL-48032 behat: Updated composer to point to v1.29.0
MDL-30968 mod/forum Fixed group link
MDL-48041 messages: Removed HTML table around user images
MDL-47391 Update pagelayout for default profile configuration
MDL-39692 grade: Ability to delete letter boundary
MDL-39692 grade: Little code clean up of letter boundary deletion
MDL-43205 user profile fields: Menu multi-lang improvements.

Improve custom user profile multi-language menu options
support, so that it is not set to a specific language.
MDL-39376 enrol: Optimized setting for ldap and database
MDL-48156 task: Skip the scheduled task only for really disabled plugins
MDL-48093 HTML 5 video: Firefox now supports .mp4
MDL-48143 backup: Bump release to 2.9 dev branch
Merge branch 'MDL-48143' of git://github.com/stronk7/moodle
MDL-47527 gradebook: Allow access to overview report
MDL-48144 upgrade: add v2.8.0 sep lines
MDL-48168 quiz editing: max grade should be editable after attempts

Note that there was a lot of legacy code left from Moodle 2.7 which is
no longer required, and I took this opportunity to delete it.