implementation for VALARM

[jonnytest1]

https://www.kanzaki.com/docs/ical/valarm.html

according to this spec (which is also supported by google with private calender export)
alarms are added like this:

BEGIN:VEVENT
SUMMARY:event summary
...
BEGIN:VALARM
ACTION:DISPLAY
TRIGGER:-P0DT0H30M0S // 30 minutes prior
DESCRIPTION:This is an event reminder
END:VALARM
BEGIN:VALARM
ACTION:DISPLAY
TRIGGER:-P3D // 3 days prior
DESCRIPTION:This is an event reminder
END:VALARM
END:VEVENT

currently they are just parsed as uuids

ideally i think they should not only be parsed but also a utility method added to get the TRIGGER correctly parsed resulting in a Date object (similarly to rrule)

(
there is also non-relative alarms in the form of trigger: P0DT9H0M0S meaning it would be on the day of the event at 9 o clock
my solution for this part looked like this since i already made the relative implementation

const copy = new Date(start_or_rrule_date);
copy.setHours(0)
copy.setMinutes(0)
copy.setSeconds(0)

return  new Date(+copy + this.timeOffset)

)

[titanism]

PR would be awesome for this 🔥

[jonnytest1]

#299