Fixing sunday logic for top5 licenses and details.

@YolinaS, @phss
Extracted week date range to a common class.

@YolinaS
@phss
Supplying weeks ago to lastWeekDateRange() and use it on
conversioncollection.

@phss
Making Sunday and Monday more explicit.

@phss
Test dates in UTC.
Forgot to properly require the date range.

@phss, @YolinaS
Refactor specs to add a date matcher to remove duplication.

@YolinaS, @phss
Adding a function for last week's date range on the Collection.
Merge pull request #129 from alphagov/fix_sunday_last_week_bug

Fix sunday last week bug