DONOTMERGE - Guillaume works

Brake compatibilities with actual cozy-calendar and actual cozy-sync, to achieve these :
* changed date convention in database: data and API is in UTC, the client has the Cozy's timezone
* client's dates are now handled with moment-timezone
* added all-day events support
* added event's reminder support


We cant have proper validation in the constructor, as the parser is built as a stream reader. The components are used in two ways :
1/ To write ICAL
new VEvent(a, b, c, d, e, f, g)

2/To read ICAL
ev = new VEvent()
ev.fields.SUMMARY = x
ev.field.LO.....

If we want proper validatoin, it will be in the toString method.
Guillaume's way of doing things make sense, just make the comment more explicit : "During parsing, VEvent are initialized without any property, so we skip the processing below" and explicitly ```return this```