The receipt email that SOGo generates and sends to the organizer
after they create a new calendar event with attendees, displays
an empty table in case the attendees have no display name. The
email address is only used in an a tag's href attribute which is
not visible to the user when the HTML email is rendered.
This commit adapts SOGoAptMailReceipt.wox to use the email address
as content of the a tags in case the display name is not set. This
is done in the same way as SOGoAptMailReminder.wox already does it.
Notifications about Modifications don't show the Calendar name.
When an email notification is selected by the user, the calendar name
from which the event was changed is added to the email.
Needs to be translated.