Improve session handling.

src/main/scala/util/Implicits.scala

@@ -54,10 +54,19 @@ object Implicits {
   }
 
   implicit class RichSession(session: HttpSession){
+
     def putAndGet[T](key: String, value: T): T = {
       session.setAttribute(key, value)
       value
     }
+
+    def getAndRemove[T](key: String): Option[T] = {
+      val value = session.getAttribute(key).asInstanceOf[T]
+      if(value == null){
+        session.removeAttribute(key)
+      }
+      Option(value)
+    }
   }
 
 }