Merge pull request #278 from markguinn/patch-print-order-fix

Fixed bug when printing order in admin
Added ability to update ProductCategory_Controller's ListSorter
Fixed pagination, sorting etc by creating/requiring a special kind of 'SQLQueryLsit'
Fixed product report link
Removed Week grouping code
FIX: start/end dates in ShopPeriodReports weren't being used in the correct format.
FIX: missing member breaks parameterFields function in unit tests
FIX: omnipay's transactionId represents the order reference.
The transactionReference should be reserved for data that gateways return.
Converted CheckoutStep continue_anchor to yaml config
FIX: ShopPeriodReport SQLQueryList closure should be php 5.3 compatible.
FIX: shop period report was failing in postgres
Added test to reveal issue with ShopPeriodReport in prostgres
Check if buyable exists before getting image from it (OrderItem->Image)
Fixes #248
merge