Add a 'week' parameter to limit to a specific week
Fix the `week` behavour to match api2
Give the WeekColumnClause funcs unique names.

This makes it much easier to test them individually.
Add test coverage for the week-related code.
Merge branch 'fix_test_coverage' into filter-by-week2
Merge pull request #156 from mreid-moz/filter-by-week2

Add a 'week' parameter to limit to a specific week