PHP7-ify the Order Line classes

This PR gets the Order Line classes written in PHP7 style for better type hinting, error checking, etc. I'll be going through the rest of the classes doing the same, but doing separate PRs for each so that there aren't 20+ changed files.

Please review: @ahoffmann @weizhong-wang @lloyd-carter @KJOYNER

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

@@ -21,7 +21,7 @@ class MockOrderLineService implements OrderLineService, MockService
     }
 
     /** @inheritdoc */
-    public function createOrderLine(OrderLine $orderLine)
+    public function createOrderLine(OrderLine $orderLine): OrderServiceResponse
     {
         return $this->response;
     }