Hide user avatars from screen readers in group and room user lists.

Like in pill components, these only duplicate information for screen readers, so hide them.

Signed-off-by: Marco Zehe <marcozehe@mailbox.org>

src/components/views/groups/GroupMemberTile.js

@@ -59,7 +59,7 @@ export default createReactClass({
         );
 
         const av = (
-            <BaseAvatar
+            <BaseAvatar aria-hidden="true"
                 name={this.props.member.displayname || this.props.member.userId}
                 idName={this.props.member.userId}
                 width={36} height={36}