Group Presence Period repeat only for the duration of the Group Calendar Assignment

We should be able to configure a group calendar saying that the pattern
is "from 9:00 to 12:00, repeat every monday morning" with a group
calendar assignment saying "use this pattern from 01/01/2016 until
31/12/2016" and then create another group calendar assignment for 2017
without having to change the periodicity stop date on all presence
periods of the group calendar.

I think it should repeat from group calendar assignment's start date
until min(group calendar assignment's stop date, presence period's
periodicity stop date).


/reviewed-on nexedi/erp5!125