Alternative construction

[oliemansm]

fixes #60

This PR provides simplifies the construction of the GraphQL Servlet and provides an alternative way as well through the proposed getConfiguration() method.

To create a new servlet you have two options. If you just want to use default settings and expose a schema use GraphQLHttpServlet.with(graphqlSchema).

If you want to control all the options use GraphQLHttpServlet.with(graphqlConfiguration). The configuration basically is the replacement for the Builder with the same functionality.

As per the suggestion in #60 you can also subclass GraphQLHttpServlet and override the getConfiguration() method as follows.

@WebServlet(name = "HelloServlet", urlPatterns = {"graphql"}, loadOnStartup = 1)
public class HelloServlet extends GraphQLHttpServlet {

  @Override
  protected GraphQLConfiguration getConfiguration() {
    return GraphQLConfiguration.with(createSchema()).build();
  }

  private GraphQLSchema createSchema() {
    String schema = "type Query{hello: String}";

    SchemaParser schemaParser = new SchemaParser();
    TypeDefinitionRegistry typeDefinitionRegistry = schemaParser.parse(schema);

    RuntimeWiring runtimeWiring = newRuntimeWiring()
        .type("Query", builder -> builder.dataFetcher("hello", new StaticDataFetcher("world")))
        .build();

    SchemaGenerator schemaGenerator = new SchemaGenerator();
    return schemaGenerator.makeExecutableSchema(typeDefinitionRegistry, runtimeWiring);
  }

}

For now the previous functionality has been deprecated. So no breaking changes yet.