src/gui/gcal-event-widget.c: Fix of slanted edges
When the event is all day, the time zone of the event and the widget does not match. This causes slanted edges to be incorrectly applied, see #109 and part of #589 (closed).
To fix, use gcal_date_time_compare_date for all day events.
src/gui/views/gcal-year-view.c: Fix of all day events showing up after end date
When event is all day, it shows up in the year view after the event ends, see #589 (closed).
Reason: as all day events end at midnight, gcal_date_time_compare_date thinks it is the next day.
To fix, substract one second before checking the date.