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/UserApi.scala

@@ -0,0 +1,58 @@
+package api
+
+import model.User
+
+@javax.annotation.Generated(value = Array("org.openapitools.codegen.languages.ScalaPlayFrameworkServerCodegen"), date = "2019-03-26T16:21:58.590+08:00[Asia/Hong_Kong]")
+trait UserApi {
+  /**
+    * Create user
+    * This can only be done by the logged in user.
+    * @param body Created user object
+    */
+  def createUser(body: User): Unit
+
+  /**
+    * Creates list of users with given input array
+    * @param body List of user object
+    */
+  def createUsersWithArrayInput(body: List[User]): Unit
+
+  /**
+    * Creates list of users with given input array
+    * @param body List of user object
+    */
+  def createUsersWithListInput(body: List[User]): Unit
+
+  /**
+    * Delete user
+    * This can only be done by the logged in user.
+    * @param username The name that needs to be deleted
+    */
+  def deleteUser(username: String): Unit
+
+  /**
+    * Get user by user name
+    * @param username The name that needs to be fetched. Use user1 for testing.
+    */
+  def getUserByName(username: String): User
+
+  /**
+    * Logs user into the system
+    * @param username The user name for login
+    * @param password The password for login in clear text
+    */
+  def loginUser(username: String, password: String): String
+
+  /**
+    * Logs out current logged in user session
+    */
+  def logoutUser(): Unit
+
+  /**
+    * Updated user
+    * This can only be done by the logged in user.
+    * @param username name that need to be deleted
+    * @param body Updated user object
+    */
+  def updateUser(username: String, body: User): Unit
+}