Minor enhancements to Scala Play server generator (#2512)

* minor enhancements to openapi-generator

* update doc

* remove oudated doc

samples/server/petstore/scala-play-server/app/api/PetApiImpl.scala

@@ -0,0 +1,83 @@
+package api
+
+import model.ApiResponse
+import model.Pet
+import play.api.libs.Files.TemporaryFile
+
+/**
+  * Provides a default implementation for [[PetApi]].
+  */
+@javax.annotation.Generated(value = Array("org.openapitools.codegen.languages.ScalaPlayFrameworkServerCodegen"), date = "2019-03-26T16:21:58.590+08:00[Asia/Hong_Kong]")
+class PetApiImpl extends PetApi {
+  /**
+    * @inheritdoc
+    */
+  override def addPet(body: Pet): Unit = {
+    // TODO: Implement better logic
+
+    
+  }
+
+  /**
+    * @inheritdoc
+    */
+  override def deletePet(petId: Long, apiKey: Option[String]): Unit = {
+    // TODO: Implement better logic
+
+    
+  }
+
+  /**
+    * @inheritdoc
+    */
+  override def findPetsByStatus(status: List[String]): List[Pet] = {
+    // TODO: Implement better logic
+
+    List.empty[Pet]
+  }
+
+  /**
+    * @inheritdoc
+    */
+  override def findPetsByTags(tags: List[String]): List[Pet] = {
+    // TODO: Implement better logic
+
+    List.empty[Pet]
+  }
+
+  /**
+    * @inheritdoc
+    */
+  override def getPetById(petId: Long): Pet = {
+    // TODO: Implement better logic
+
+    Pet(None, None, "", List.empty[String], None, None)
+  }
+
+  /**
+    * @inheritdoc
+    */
+  override def updatePet(body: Pet): Unit = {
+    // TODO: Implement better logic
+
+    
+  }
+
+  /**
+    * @inheritdoc
+    */
+  override def updatePetWithForm(petId: Long, name: Option[String], status: Option[String]): Unit = {
+    // TODO: Implement better logic
+
+    
+  }
+
+  /**
+    * @inheritdoc
+    */
+  override def uploadFile(petId: Long, additionalMetadata: Option[String], file: Option[TemporaryFile]): ApiResponse = {
+    // TODO: Implement better logic
+
+    ApiResponse(None, None, None)
+  }
+}