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


What do you think of
```coffeescript
rrule = rrule.split ';'
           .filter (s) -> s.indexOf('DTSTART') isnt 0
           .join ';'
```
(comment is good, nice)