First pass on separating stm into its own module

- removed transactors everywhere
- moved stm into akka-stm module
- disabled agents (they use transactors internally)
- rewrote persistence tests so that they don't use transactors

akka-actor/src/test/java/akka/stm/RefExample.java

@@ -1,36 +0,0 @@
-package akka.stm;
-
-import akka.stm.Ref;
-import akka.stm.local.Atomic;
-
-public class RefExample {
-    public static void main(String[] args) {
-        System.out.println();
-        System.out.println("Ref example");
-        System.out.println();
-
-        final Ref<Integer> ref = new Ref<Integer>(0);
-
-        Integer value1 = new Atomic<Integer>() {
-            public Integer atomically() {
-                return ref.get();
-            }
-        }.execute();
-
-        System.out.println("value 1: " + value1);
-
-        new Atomic() {
-            public Object atomically() {
-                return ref.set(5);
-            }
-        }.execute();
-
-        Integer value2 = new Atomic<Integer>() {
-            public Integer atomically() {
-                return ref.get();
-            }
-        }.execute();
-
-        System.out.println("value 2: " + value2);
-    }
-}