Add support for Jackson 2.7

AbstractJackson2HttpMessageConverter now implements its own
TypeVariable resolution algorithm since in Jackson 2.7 it is now
deprecated and has not the same behavior .
See https://github.com/FasterXML/jackson-databind/issues/1087
for more details.

The dependency on jackson-datatype-jdk7 has been removed since
it is now provided by default in the jackson-databind module.

Issues: SPR-13483, SPR-13728

spring-web/src/test/java/org/springframework/http/converter/json/SpringHandlerInstantiatorTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2016 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -218,10 +218,15 @@ public class SpringHandlerInstantiatorTests {
 			return null;
 		}
 
-		// New in Jackson 2.5
+		@Override
 		public JavaType typeFromId(DatabindContext context, String id) {
 			return null;
 		}
+
+		// New in Jackson 2.7
+		public String getDescForKnownTypeIds() {
+			return null;
+		}
 	}