[FIX] google_calendar: recurrent event syncrhonization

When an attendee is added exceptionnally in an instance of a recurrent event, do not try to sync the basic recurrent event in his calendar
[FIX] google_calendar: deleted excluded recurring event

Do not try to delete an excluded recurrent event added in Google, but not yet syncrhonised in Odoo (immediately deleted for instance)
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-win32