Make translatable captions

Make translatable captions in:

oscar/apps/offer/models.py
oscar/templates/oscar/customer/notifications/list.html
oscar/templates/oscar/dashboard/orders/order_list.html
oscar/templates/oscar/dashboard/ranges/range_list.html
oscar/templates/oscar/dashboard/users/index.html
oscar/templates/oscar/dashboard/vouchers/voucher_detail.html
oscar/templates/oscar/dashboard/vouchers/voucher_list.html
oscar/templates/oscar/dashboard/reviews/review_list.html