Closing #264, addign JavaAPI to DataFlowVariable

akka-actor/src/main/scala/util/JavaAPI.scala

@@ -13,4 +13,11 @@ trait Function[T,R] {
  */
 trait Procedure[T] {
   def apply(param: T): Unit
-}
+}
+
+/**
+ * An executable piece of code that takes no parameters and doesn't return any value
+ */
+trait SideEffect {
+  def apply: Unit
+}