!per #15230 rename processorId => persistentId

* This is NOT binary compatible, we're in an *experimental* module.
* disabled binary compat checks for package akka.persistence
* Source compatibility is retained, but users should migrate do the new
  method name ASAP.
* Plugin APIs were migrated in a way that allows the old plugins to
  compile agains 2.3.4 without having to change anything. Hopefuly this
  will help authors migrate to 2.3.4 sooner. This is only source level compatible, not binary compatible.
* added deprecation warnings on all processorId methods and provided bridges where possible
* for users, the migration should be painless, they can still override
  the old method, and it'll work. But we encourage them to move to
  persistenceId; All delegation code will have to be removed afterwards ofc.

Conflicts:
	akka-persistence/src/main/scala/akka/persistence/Channel.scala
	akka-persistence/src/main/scala/akka/persistence/JournalProtocol.scala
	akka-persistence/src/main/scala/akka/persistence/Persistent.scala
	akka-persistence/src/main/scala/akka/persistence/PersistentChannel.scala
	akka-persistence/src/main/scala/akka/persistence/Processor.scala
	akka-persistence/src/main/scala/akka/persistence/Snapshot.scala
	akka-persistence/src/main/scala/akka/persistence/journal/AsyncWriteProxy.scala
	akka-persistence/src/main/scala/akka/persistence/journal/inmem/InmemJournal.scala
	akka-persistence/src/main/scala/akka/persistence/journal/leveldb/LeveldbKey.scala
	akka-persistence/src/main/scala/akka/persistence/snapshot/SnapshotStore.scala
	akka-persistence/src/test/scala/akka/persistence/serialization/SerializerSpec.scala
	project/AkkaBuild.scala

akka-docs/rst/java/code/docs/persistence/PersistencePluginDocTest.java

@@ -53,7 +53,7 @@ public class PersistencePluginDocTest {
 
     class MySnapshotStore extends SnapshotStore {
         @Override
-        public Future<Option<SelectedSnapshot>> doLoadAsync(String processorId, SnapshotSelectionCriteria criteria) {
+        public Future<Option<SelectedSnapshot>> doLoadAsync(String persistenceId, SnapshotSelectionCriteria criteria) {
             return null;
         }
 
@@ -71,7 +71,7 @@ public class PersistencePluginDocTest {
         }
 
         @Override
-        public void doDelete(String processorId, SnapshotSelectionCriteria criteria) throws Exception {
+        public void doDelete(String persistenceId, SnapshotSelectionCriteria criteria) throws Exception {
         }
     }
 
@@ -87,22 +87,22 @@ public class PersistencePluginDocTest {
         }
 
         @Override
-        public Future<Void> doAsyncDeleteMessages(Iterable<PersistentId> messageIds, boolean permanent) {
+        public Future<Void> doAsyncDeleteMessages(Iterable<PersistenceId> messageIds, boolean permanent) {
             return null;
         }
 
         @Override
-        public Future<Void> doAsyncDeleteMessagesTo(String processorId, long toSequenceNr, boolean permanent) {
+        public Future<Void> doAsyncDeleteMessagesTo(String persistenceId, long toSequenceNr, boolean permanent) {
             return null;
         }
 
         @Override
-        public Future<Void> doAsyncReplayMessages(String processorId, long fromSequenceNr, long toSequenceNr, long max, Procedure<PersistentRepr> replayCallback) {
+        public Future<Void> doAsyncReplayMessages(String persistenceId, long fromSequenceNr, long toSequenceNr, long max, Procedure<PersistentRepr> replayCallback) {
             return null;
         }
 
         @Override
-        public Future<Long> doAsyncReadHighestSequenceNr(String processorId, long fromSequenceNr) {
+        public Future<Long> doAsyncReadHighestSequenceNr(String persistenceId, long fromSequenceNr) {
             return null;
         }
     }