Fix start dates following migration

The migration of dataset parameters caused an hour of timezone-ness to get added to the dates. This resulted in the first data point of the sets to return "no-data" (since I assume the monthly data is all in the database at a timestamp of midnight on the first of the month)
Fix chrome bug where border top was disappearing after sort
Merge pull request #681 from alphagov/bugfix/timezone-weirdness

Fix start dates following migration
Merge pull request #684 from alphagov/bugfix/sortable-tables-border

Fix chrome bug where border top was disappearing after sort