Messaging: add aria-label to sections to explain the meaning of the numbers

Please test these UI changes on: Clean (3.6), Classic (master) and Boost (3.6 and master) themes Supported browsers Viewing the page html code using each browser facilites (Inspector...). Setup Log in as an admin Create a course C1 Enrol students s1, s2 and s3 to C1 Create group g1 and enable group messaging Add s1, s2 and s3 to g1 Logout Log in as s1 Send some messages to s2 Send some messages to s3 Send some messages to g1 Send a contact request to s2 Star s2 conversation Log out. Log in as s2 Accept s1 contact request Send some messages to s1 Send some messages to g1 Log out. Log in as s3 Send a Contact request to s1 Send some messages to s1 Send some messages to g1   Testing scenario 1: Overview Log in as s1 CHECK the number over the notifications icon with the data-region="count-container" has the aria-label="There are x unread notifications" attribute CHECK the number over the message icon with the data-region="count-container" has the aria-label="There are x unread conversations" attribute Open the message drawer CHECK the number near the Contacts with  data-region="contact-request-count" has the  aria-label="There are x pending contact requests" attribute For each section (Starred, Group and Private): CHECK the element containing the total conversations ( data-region="section-total-count-container" ) has the  aria-label="There are x total conversations" attribute CHECK the element containing the unread conversations ( data-region="section-unread-count" ) has the  aria-label="There are x unread conversations" attribute CHECK the conversations with unread messages have the  aria-label="There are 2 unread messages" in the element  data-region="unread-count" CHECK the last date message element ( data-region="last-message-date" ) has the  aria-hidden="true"  attribute