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/CounterExample.java

@@ -1,26 +0,0 @@
-package akka.stm;
-
-import akka.stm.Ref;
-import akka.stm.local.Atomic;
-
-public class CounterExample {
-    final static Ref<Integer> ref = new Ref<Integer>(0);
-
-    public static int counter() {
-        return new Atomic<Integer>() {
-            public Integer atomically() {
-                int inc = ref.get() + 1;
-                ref.set(inc);
-                return inc;
-            }
-        }.execute();
-    }
-
-    public static void main(String[] args) {
-        System.out.println();
-        System.out.println("Counter example");
-        System.out.println();
-        System.out.println("counter 1: " + counter());
-        System.out.println("counter 2: " + counter());
-    }
-}