Fix queries

Apparently SQLAlchemy does not like queries with 'is not None' so
they are changed back to '!= None'.

There was a bug in get_active_regular_meeting which was checking
if the end of the regular meeting is after the end of the week, this
leading to the meeting not showing up in its last week.
Fix get_regular_meeting_at_date for the change on get_active_regular_meeting

Hourra for the unit-tests!
Merge pull request #6 from fedora-infra/fix_queries

Fix queries