Author: Ryan Wyllie
MDL-55972 message: confirmation modal when deleting conversation
http://git.moodle.org/gw?p=moodle.git;a=commit;h=9d8f6f4af016424f15bb106b5a11b60e036361d5
http://github.com/moodle/moodle/commit/9d8f6f4af016424f15bb106b5a11b60e036361d5
+ 3.2 en [deleteallconfirm,core_message]