Improve the group messaging digest email html

Prerequisites. Set-up mailcatcher ( https://mailcatcher.me/ ). Log in as an admin. Visit ‘Site administration’ > ‘Server’ > ‘Outgoing mail configuration’. Set the 'SMTP hosts' field to '127.0.0.1:1025' and save. Visit http://127.0.0.1:1080/ in your browser so you can view outgoing emails. Create a new course C1. Create 2 users "Student number one"  and "Student number two" Create a group "Users Group G1" with a group picture and messaging enabled Add users "Student number one"  and "Student number two" to group "Users Group G1" Navigate to 'Site Administration > Tasks > Scheduled tasks" Find "Messages digest mailings" and click the gear icon Insert and asterix in all fields. ( * ) and save changes. Test 1 Log in as Student number one. Send 3 messages to the "Users Group G1" Log out Run the following:  php admin/tool/task/cli/schedule_task.php --execute="\message_email\task\send_email_task"   Confirm Student number two gets an email. Confirm the email is styled like the attached design in this issue.