Fluent API for JsonObject and JsonArray and JsonObject.getOrElse() method

Enhancements:

- Upgraded language version to Java 8
- Upgraded maven plugins

- JsonObject can now be constructed via factory method: jsonObject(); // Can be statically imported
- JsonArray can now be constructed via factory method: jsonArray(); // Can be statically imported

- JsonObject.getOrElse(name, defaultValue)  // returns default value when name is not found.