MDL-38102 lib: Check for null return value from password_hash function call
MDL-38500 repository: Instance names must be unique
MDL-39448 MUC: Memcache configurable key names
MDL-39452 Library: html_writer::attribute unnecessary is_array check
MDL-38979 Add lang menu to empty custommenu

Show custom menu even when no custom menu items if lang menu needs
to be shown.
MDL-39388 bootstrapbase: Add bootstrap tab renderer

This adds a renderer that outputs standard bootstrap HTML for tabs,
deletes styles that were previously required to make Moodle tab HTML
superficially resemble Bootstrap, and tweak the responsive code that
makes tabs stack on phones to account for the change too.
MDL-39436 fixing RTL in filemanager
MDL-39332 Formslib: remove z-index from calendar panel

calendar panel.render() sets zIndex to 0, when calendar is used next to filepicker, it overlaps
zIndex should be set by css and not JS, and previously used removeAttr on panel breaks JS on ie8.
So solution is to render panel and then remove z-index from dom
MDL-39481 behat: Provide info about init.php
MDL-39482 avoid using get_category_or_system_context() because file might not be included
MDL-39187 forms: fixed issue where calendar pop-up did not display when a date selector form element was added to a group
MDL-31193 display the correct and translated token valid until date
MDL-29472_m WebServices Cohorts
MDL-39496 Admin: Reduce excessive is_array tests in admin_category

admin_category::category_cache is a protected value which is only ever
treated as an array. We shouldn't need to test that it's an array each time
we use it.
MDL-39497 Consider workshop scheduled allocator stable
MDL-30130 bootstrapbase: Bring back Quiz answer feedback
MDL-39499 bootstrapbase: Make two .singlebuttons line up
MDL-39364 theme_clean: remove all references to the Simple theme from Clean theme.
MDL-39482 avoid using get_category_or_system_context() because file might not be included
MDL-38596 Optimise SQL in preloading course contacts for number of courses