ENH: Add Query findEach() with batch consumer

This is a variation of findEach() that makes it easy to have a batch consumer processing a large result in batches.  For example, process in batches of 50 beans.

Note that the last batch consumed/processed will often have less than the batch size.

ebean-api/src/main/java/io/ebean/ExpressionList.java

@@ -307,6 +307,13 @@ public interface ExpressionList<T> {
    */
   void findEach(Consumer<T> consumer);
 
+  /**
+   * Execute findEach with a batch consumer.
+   *
+   * @see Query#findEach(int, Consumer)
+   */
+  void findEach(int batch, Consumer<List<T>> consumer);
+
   /**
    * Execute the query processing the beans one at a time with the ability to
    * stop processing before reading all the beans.

ebean-api/src/main/java/io/ebean/ExtendedServer.java

@@ -159,6 +159,13 @@ public interface ExtendedServer {
    */
   <T> void findEach(Query<T> query, Consumer<T> consumer, Transaction transaction);
 
+  /**
+   * Execute findEach with batch consumer.
+   *
+   * @see Query#findEach(int, Consumer)
+   */
+  <T> void findEach(Query<T> query, int batch, Consumer<List<T>> consumer, Transaction t);
+
   /**
    * Execute the query visiting the each bean one at a time.
    * <p>

ebean-api/src/main/java/io/ebean/Query.java

@@ -810,7 +810,7 @@ public interface Query<T> {
    * </p>
    * <p>
    * This method is functionally equivalent to findIterate() but instead of using an
-   * iterator uses the Consumer interface which is better suited to use with Java8 closures.
+   * iterator uses the Consumer interface which is better suited to use with closures.
    * </p>
    * <pre>{@code
    *
@@ -829,6 +829,21 @@ public interface Query<T> {
    */
   void findEach(Consumer<T> consumer);
 
+  /**
+   * Execute findEach streaming query batching the results for consuming.
+   * <p>
+   * This query execution will stream the results and is suited to consuming
+   * large numbers of results from the database.
+   * <p>
+   * Typically we use this batch consumer when we want to do further processing on
+   * the beans and want to do that processing in batch form, for example - 100 at
+   * a time.
+   *
+   * @param batch    The number of beans processed in the batch
+   * @param consumer Process the batch of beans
+   */
+  void findEach(int batch, Consumer<List<T>> consumer);
+
   /**
    * Execute the query using callbacks to a visitor to process the resulting
    * beans one at a time.
@@ -839,12 +854,12 @@ public interface Query<T> {
    * </p>
    * <p>
    * This method is functionally equivalent to findIterate() but instead of using an
-   * iterator uses the Predicate (SAM) interface which is better suited to use with Java8 closures.
+   * iterator uses the Predicate interface which is better suited to use with closures.
    * </p>
    * <pre>{@code
    *
    *  DB.find(Customer.class)
-   *     .fetch("contacts", FetchConfig.ofQuery(2))
+   *     .fetchQuery("contacts")
    *     .where().eq("status", Status.NEW)
    *     .order().asc("id")
    *     .setMaxRows(2000)