add trading managers

src/main/java/TradingManager.java

@@ -0,0 +1,13 @@
+import ats.orders.OrderRequest;
+
+/**
+ * TradingManager describes the interface with a trading system.
+ */
+interface TradingManager {
+
+    /**
+     * Place an order request.
+     */
+    public void placeOrder(OrderRequest order);
+
+}