Update Neo4j extension to use Spring Data Neo4j. (#125)

Move away from the Neo4j OGM usage because Spring Data Neo4j
fits better in the ecosystem, spring-batch is settled in.

Previously there was no visible difference to users because Spring Data Neo4j
was based on Neo4j OGM which isn't the case anymore.

spring-batch-neo4j/README.md

@@ -7,16 +7,11 @@ This extension contains an `ItemReader` and `ItemWriter` implementations for [Ne
 The `Neo4jItemReader` can be configured as follows:
 
 ```java
-SessionFactory sessionFactory = ...
-Neo4jItemReader<String> itemReader = new Neo4jItemReaderBuilder<String>()
-        .sessionFactory(sessionFactory)
-        .name("itemReader")
-        .targetType(String.class)
-        .startStatement("n=node(*)")
-        .orderByStatement("n.age")
-        .matchStatement("n -- m")
-        .whereStatement("has(n.name)")
-        .returnStatement("m")
+Neo4jItemReader<User> reader = new Neo4jItemReaderBuilder<User>()
+        .neo4jTemplate(neo4jTemplate)
+        .name("userReader")
+        .statement(Cypher.match(userNode).returning(userNode))
+        .targetType(User.class)
         .pageSize(50)
         .build();
 ```
@@ -24,8 +19,93 @@ Neo4jItemReader<String> itemReader = new Neo4jItemReaderBuilder<String>()
 The `Neo4jItemWriter` can be configured as follows:
 
 ```java
-SessionFactory sessionFactory = ...
-Neo4jItemWriter<String> writer = new Neo4jItemWriterBuilder<String>()
-        .sessionFactory(sessionFactory)
+Neo4jItemWriter<User> writer = new Neo4jItemWriterBuilder<User>()
+        .neo4jTemplate(neo4jTemplate)
+        .neo4jDriver(driver)
+        .neo4jMappingContext(mappingContext)
         .build();
+```
+
+## Minimal Spring Boot example
+
+Additional to the already existing dependencies in a new Spring Boot application,
+`spring-boot-starter-data-neo4j`, `spring-batch-neo4j` and the `spring-boot-starter-batch` are needed 
+but `spring-jdbc` and `spring-boot-starter-jdbc` must be explicitly excluded.
+The exclusions are mandatory to avoid any need for JDBC-based connections, like JDBC URI etc.
+
+See the following _build.gradle_ dependency definition for a minimal example.
+
+```groovy
+dependencies {
+    implementation ('org.springframework.boot:spring-boot-starter-batch') {
+        exclude group: 'org.springframework', module: 'spring-jdbc'
+        exclude group: 'org.springframework.boot', module: 'spring-boot-starter-jdbc'
+    }
+    // current development version 0.2.0-SNAPSHOT
+    implementation 'org.springframework.batch.extensions:spring-batch-neo4j'
+    implementation 'org.springframework.boot:spring-boot-starter-data-neo4j'
+    testImplementation 'org.springframework.boot:spring-boot-starter-test'
+    testImplementation 'org.springframework.batch:spring-batch-test'
+}
+```
+
+An example of the usage can be seen in the following example, implementing the `CommandLineRunner` interface.
+
+```java
+@SpringBootApplication
+public class TestSpringBatchApplication implements CommandLineRunner {
+    // those dependencies are created by Spring Boot's
+    // spring-data-neo4j autoconfiguration
+    @Autowired
+    private Driver driver;
+    @Autowired
+    private Neo4jMappingContext mappingContext;
+    @Autowired
+    private Neo4jTemplate neo4jTemplate;
+  
+    public static void main(String[] args) {
+      SpringApplication.run(TestSpringBatchApplication.class, args);
+    }
+  
+    @Override
+    public void run(String... args) {
+      // writing
+      Neo4jItemWriter<User> writer = new Neo4jItemWriterBuilder<User>()
+        .neo4jTemplate(neo4jTemplate)
+        .neo4jDriver(driver)
+        .neo4jMappingContext(mappingContext)
+        .build();
+      writer.write(Chunk.of(new User("id1", "ab"), new User("id2", "bb")));
+      
+      // reading
+      org.neo4j.cypherdsl.core.Node userNode = Cypher.node("User");
+      Neo4jItemReader<User> reader = new Neo4jItemReaderBuilder<User>()
+        .neo4jTemplate(neo4jTemplate)
+        .name("userReader")
+        .statement(Cypher.match(userNode).returning(userNode))
+        .targetType(User.class)
+        .build();
+      List<User> allUsers = new ArrayList<>();
+      User user = null;
+      while ((user = reader.read()) != null) {
+        System.out.printf("Found user: %s%n", user.name);
+        allUsers.add(user);
+      }
+      
+      // deleting
+      writer.setDelete(true);
+      writer.write(Chunk.of(allUsers.toArray(new User[]{})));
+    }
+  
+    @Node("User")
+    public static class User {
+      @Id public final String id;
+      public final String name;
+      
+      public User(String id, String name) {
+        this.id = id;
+        this.name = name;
+      }
+    }
+}
 ```