MDL-40515: report_log: List activities in optgroups
MDL-42111 TinyMCE media preview: fix video preview display for TinyMCE media.

Effected themes: boxxie, clean, brick, formal_white and splash.
MDL-38664 Lesson mod: fixed re-attempt unseen page
MDL-38664 Lesson mod: code improvement for lesson re-attempt page
MDL-42453 theme_base: Fixed Error in base/style/admin.css that breaks CSS validator.
MDL-42465 mod_chat: instantiated message object before declaring properties
MDL-42489 backup: use correct exception class in automated backups
MDL-42494 Fix workshop coding exception if all assessments have zero weight

If all assessments for the given submission have zero weight, the grading
evaluation plugin "Comparison with the best assessment" is unable to decide on
the average assessment as it ignores those with zero weight. In such rare case,
it makes sense to set the grading grade to null and prevent the coding
exception.
MDL-34654 Glossary: ampersand breaks auto-linking
MDL-42533 conditionlib: Field name is translated for students
MDL-42270 course: Section name too big message.
MDL-42548 quiz review: don't show grade for non-finished attempts.

Now we show the attempt state separately, so there is no need to show
Grade: Attempt still in progress - especially since we were showing that
for abandoned and overdue attempts which is just wrong.
MDL-42551 timezone info: updated to 2013h
MDL-38850: Fixed Horizontal bar issue in lesson
MDL-35146 mod_wiki: fixed issue where pages for deleted groups caused an error on restore
MDL-35146 mod_wiki: fixed variable typo and altered code to conform to Moodle guidelines
MDL-28463 conditionlib: 10 minutes lifetime of cached grades
MDL-42604 scorm: Fix division by zero warnings in error logs
MDL-42613 core_group: removed unnecessary table row when there is no group description or picture
MDL-42605 portfolio_flickr: Photos can be added to a set on export