MDL-46302 correct atto img float right

Correct the atto image "float right" margin CSS
MDL-46552 session: add support for multiple servers in memcached session driver
MDL-46775: Fix call to unavailable function when loading an invalid JS file
Normalize request header names.
MDL-46760 mod_scorm: Fix js error when preview mode disabled
MDL-44894 question editing: fix validation with odd permissions

For users with edit permissions, but not add permissions, it was
impossible to save the editing form. The validation assuemd this value
was present, but it was not. Other code checks this field too, so I
added it rather than changing the validation and all the other uses.
MDL-46791 question: fixed incorrect 5th param for tag_set()
MDL-46281 core_backup: Add class_exists check for backup_<mod>_activity_task

Signed-off-by: Tony Butler <tonyjbutler@gmail.com>
MDL-46829 theme_base: Fixed regression in Base casued by MDL-45031.
MDL-46188 course:show/hide button disappears after action
MDL-46833 mod_assign: Fix assignment view when available for group members only.

When assignment is "Available for group members only" and no users with
mod/assign:submit role permision is enrolled (students),
groups_filter_users_by_course_module_visible is causing error (as $users
array is empty). The patch resolves the issue.
MDL-41513 mod_quiz: Scrollbar not working in JS Security Popup
MDL-46826 forum: make sql query indexed, regression from MDL-31089
MDL-46817 behat: Table selector support css

Previously table selector supported id and caption only.
But in few cases we don't have proper id, so added support
for css
MDL-45874 Fix access to users reports in navigation when using separate groups
MDL-46538 theme_base/theme_bootstrapbase: Removed incorrect RTL CSS.
MDL-46589 scheduled task does not send emails

Thanks to  Luděk Šulák  for the patch
Automatically generated installer lang files
MDL-46817 behat: Step to check if value exist/not in table column
Merge branch 'm27_MDL-46760' of https://github.com/danmarsden/moodle into MOODLE_27_STABLE