Setup Gradle multi-module build

Added core, config and samples modules. Moved sample project into samples module.

Closes gh-10

samples/helloworld/spring-authorization-server-samples-helloworld.gradle

@@ -0,0 +1,12 @@
+apply plugin: 'io.spring.convention.spring-sample-boot'
+
+dependencies {
+	implementation 'org.springframework.boot:spring-boot-starter'
+	testImplementation('org.springframework.boot:spring-boot-starter-test') {
+		exclude group: 'org.junit.vintage', module: 'junit-vintage-engine'
+	}
+}
+
+test {
+	useJUnitPlatform()
+}

samples/helloworld/src/main/java/sample/Application.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package sample;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class Application {
+
+    public static void main(String[] args) {
+        SpringApplication.run(Application.class, args);
+    }
+}

samples/helloworld/src/test/java/sample/ApplicationTest.java

@@ -0,0 +1,16 @@
+package sample;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.context.ApplicationContext;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@SpringBootTest
+public class ApplicationTest {
+
+    @Test
+    public void loadContext(ApplicationContext context) {
+        assertThat(context).isNotNull();
+    }
+}