Author: Sara Arjona
MDL-64985 message: display aria label to the mute icon
http://git.moodle.org/gw?p=moodle.git;a=commit;h=d03f037431af52aab531af88ec7a19f55499c40a
http://github.com/moodle/moodle/commit/d03f037431af52aab531af88ec7a19f55499c40a
+ 3.7 en [mutedconversation,core_message]