Make 'slotNormal' variable in Agenda Views

Currently whenever in Agenda Views the time is displayed in every line or not is determined automatically (slotNormal = opt('slotMinutes') % 15 == 0;).

It would be nice, if one could change that by a variable. Hence, only set slotNormal = false and times are also shown for opt('slotMinutes') % 15.

The proposed code shows that only 2 lines would need to be adapted...