remove Actor.preRestart(cause: Throwable)

- adapt all internal uses (all tests green)
- start migration guide for 2.0 with this change

akka-camel/src/test/scala/akka/camel/ConsumerScalaTest.scala

@@ -254,7 +254,7 @@ object ConsumerScalaTest {
       case "succeed" ⇒ self.reply("ok")
     }
 
-    override def preRestart(reason: scala.Throwable) {
+    override def preRestart(reason: scala.Throwable, msg: Option[Any]) {
       self.reply_?("pr")
     }