Add version range support for Kotlin version

Closes gh-556

initializr-web/src/test/java/io/spring/initializr/web/project/MainControllerIntegrationTests.java

@@ -117,6 +117,14 @@ public class MainControllerIntegrationTests
 				.hasSpringBootStarterTest();
 	}
 
+	@Test
+	public void kotlinRange() {
+		downloadZip("/starter.zip?style=web&language=kotlin&bootVersion=1.2.1.RELEASE")
+				.isKotlinProject().isMavenProject()
+				.pomAssert().hasDependenciesCount(4)
+				.hasProperty("kotlin.version", "1.1");
+	}
+
 	@Test
 	public void gradleWarProject() {
 		downloadZip("/starter.zip?style=web&style=security&packaging=war&type=gradle.zip")

initializr-web/src/test/resources/metadata/config/test-default.json

@@ -37,7 +37,17 @@
       "dependencyManagementPluginVersion": "1.0.0.RELEASE"
     },
     "kotlin": {
-      "version": null
+      "defaultVersion": "1.2",
+      "mappings": [
+        {
+          "versionRange": "[1.0.0.RELEASE,1.2.0.RELEASE)",
+          "version": "1.0"
+        },
+        {
+          "versionRange": "[1.2.0.RELEASE,1.5.0.RELEASE)",
+          "version": "1.1"
+        }
+      ]
     },
     "maven": {
       "parent": {