Avoid using raw types

There's 163 warnings when open the Java Client in Eclipse IDE. Most of them is about Java generic problem. Here're the list of example warnings shown:

• NuxeoEntity is a raw type. References to generic type NuxeoEntity<T> should be parameterized
  Operation.java

  public class Operation extends NuxeoEntity {
                                           ^
  

• List is a raw type. References to generic type List<E> should be parameterized
  TestRepository.java

  List list = (List) document.getProperties().get("ds:fields");
     ^            ^
  

• Type safety: The method execute(Callback, Object...) belongs to the raw type NuxeoEntity. References to generic type NuxeoEntity<T> should be parameterized
  Repository.java

  public void fetchDocumentRoot(Callback<Document> callback) {
      execute(callback);
            ^
  }
  

• The type parameter T is hiding the type T
  NuxeoResponseConverterFactory.java

  public <T> T readJSON(Reader reader, Class javaType) {
          ^
      try {
          return (T) objectMapper.readValue(reader, javaType);
      } catch (IOException reason) {
          throw new NuxeoClientException("...", reason);
      }
  }
  

Even though these issues does not have direct impact on Nuxeo users, but the code should be refactored to ensure the good understanding of Java generic in general.