templates/schedule: Only show date on first day of each schedule

[rkdarst]

• This places the date on only the first session of each day, instead
  of on every session.
• In theory the date is needed on every row, since depending on your
  timezone different sessions on a "day" may be on different local
  days.
• But those people can probably figure out that it spans a day and
  mentally adjust. That is what would happen if it wasn't converted
  to their own timezone anyway.
• To me the benefit here is that it's easier to scan vertically and
  divide up the schedule into distinct days, and understand each day
  separately.

[rkdarst]

This is what it looks like: