PHP7-ify Order Header classes, add `ServiceResponseInterface`

src/main/edu/wisc/services/cbs/api/MockService.php

.../edu/wisc/services/cbs/common/AbstractServiceResponse.php

...edu/wisc/services/cbs/common/ServiceResponseInterface.php

...main/edu/wisc/services/cbs/order/OrderServiceResponse.php

...wisc/services/cbs/order/header/MockOrderHeaderService.php

src/main/edu/wisc/services/cbs/order/header/OrderHeader.php

...ces/cbs/order/header/OrderHeaderInputParametersMapper.php

...edu/wisc/services/cbs/order/header/OrderHeaderService.php

...wisc/services/cbs/order/header/SoapOrderHeaderService.php

...ces/cbs/order/interfacing/MockOrderInterfacingService.php

...edu/wisc/services/cbs/order/line/MockOrderLineService.php

src/main/edu/wisc/services/cbs/price/MockPriceService.php

...main/edu/wisc/services/cbs/product/MockProductService.php