Improve rendering of all-day events.

[willstott101]

Our integration is showing messages like these for all-day events:

Start: 2020-07-31 01:00:00
End: 2020-08-01 01:00:00

Would it be possible to instead show:

Full Day: 2020-07-31

and for multi-day events:

Start: 2020-07-31 01:00:00
End: 2020-08-06 01:00:00

becomes

First Day: 2020-07-31
Last Day: 2020-08-05

The current system shows the end date as after the actual event, and includes an arbitrary time in the output.