Add vaadin-core dependency and update spring.provides (#313)

Add a test that dependency is applied.
Update polymer to version 2.6.0

vaadin-spring-boot-starter/pom.xml

@@ -50,6 +50,11 @@
     </dependencyManagement>
 
     <dependencies>
+        <dependency>
+            <groupId>com.vaadin</groupId>
+            <artifactId>vaadin-core</artifactId>
+        </dependency>
+
         <!-- Spring -->
         <dependency>
             <groupId>org.springframework.boot</groupId>

vaadin-spring-boot-starter/src/main/resources/META-INF/spring.provides

@@ -1 +1 @@
-provides: flow-spring-addon, spring-boot-starter-web, flow-html-components
+provides: vaadin-spring-addon, spring-boot-starter-web, vaadin-components

vaadin-spring-tests/test-spring-boot-scan/src/main/java/com/vaadin/flow/spring/scan/test/TestServletInitializer.java

@@ -26,6 +26,7 @@
 import org.springframework.security.oauth2.config.annotation.web.configurers.AuthorizationServerEndpointsConfigurer;
 import org.springframework.security.oauth2.config.annotation.web.configurers.AuthorizationServerSecurityConfigurer;
 
+import com.vaadin.flow.component.button.Button;
 import com.vaadin.flow.spring.annotation.EnableVaadin;
 
 @SpringBootApplication
@@ -38,6 +39,9 @@ public class TestServletInitializer implements AuthorizationServerConfigurer {
 
     public static void main(String[] args) {
         SpringApplication.run(TestServletInitializer.class, args);
+        // declare here only for testing, if the vaadin-core dependency presents
+        // otherwise compilation error
+        Button button = new Button();
     }
 
     @Override

vaadin-spring-tests/test-spring-common/pom.xml

@@ -36,7 +36,7 @@
         <dependency>
             <groupId>org.webjars.bowergithub.polymer</groupId>
             <artifactId>polymer</artifactId>
-            <version>2.5.0</version>
+            <version>2.6.0</version>
         </dependency>
 
     </dependencies>