Update Jackson annotations to version 2.4 (fixes NoSuchMethodError in @JsonProperty with 2.4)

When using RestyGWT 2.0-SNAPSHOT with Jackson 2.4, if RestyGWT is first on the classpath, Jackson fails with:

```
java.lang.NoSuchMethodError: com.fasterxml.jackson.annotation.JsonProperty.index()I
```

This commit fixes the issue by updating annotations to those from Jackson 2.4, adding the missing `index()` method to `@JsonProperty`.