[Forms] Use ng-model for tree state

Use ng-model when communicating state to/from the
tree in browse mode. This will simplify implementation
of the Locator control, which also uses a tree, but
which should not set navigation state. WTD-593.

platform/representation/src/MCTRepresentation.js

@@ -141,7 +141,12 @@ define(
 
                 // Two-way bind key and parameters, get the represented domain
                 // object as "mct-object"
-                scope: { key: "=", domainObject: "=mctObject", parameters: "=" }
+                scope: {
+                    key: "=",
+                    domainObject: "=mctObject",
+                    ngModel: "=",
+                    parameters: "="
+                }
             };
         }