Fix Meeting.get_by_date

With this new query, the function retrieves all the meetings that either start or stop in
the time frame considered

Relates to https://fedorahosted.org/fedocal/ticket/61
Filter out part of meeting which do not belong to the week

This change remove from the list of meetings to display all the part of meetings that
either start earlier or end later than the week considered.
This is necessary for full day meeting starting on a Sunday.

Fixes https://fedorahosted.org/fedocal/ticket/61