DATAREST-199 - Tweaked unmarshalling of JSON payloads.

The BeanWrapper used to set and get values of entities now gets a autowired ConversionService applied. Simplified collection and map creation by using Spring API. Added test case to update an entity with an embedded collection.

spring-data-rest-webmvc/src/test/resources/org/springframework/data/rest/webmvc/jpa/order.json

@@ -0,0 +1,7 @@
+{ "creator" : {
+    "href" : "http://localhost:8080/persons/1"
+  },
+  "lineItems" : [ 
+  	{ "name" : "Java Chip" },
+  	{ "name" : "Chocolate Mocca " } ]
+}