refactor: performance improvements in batch message processing, synchronized cache access and audible message notifications.

Increase audible timeout on DefaultMessageNotifier.java, don't send in-thread notification based on last audible notification.

Create a batch message receive job to handle up to 20 chunked messages at a time per job instead of singular or open group poll amount

Remove synchronized access to recipient cache and replace with a concurrent cache that's lock free from perf tracing monitor contention

libsignal/protobuf/Makefile

@@ -1,3 +1,3 @@
 
 all:
-	protoc25 --java_out=../src/main/java/ SignalService.proto WebSocketResources.proto
+	protoc25 --java_out=../src/main/java/ SignalService.proto WebSocketResources.proto Utils.proto

libsignal/protobuf/Utils.proto

@@ -0,0 +1,10 @@
+syntax = "proto2";
+
+package signalservice;
+
+option java_package = "org.session.libsignal.protos";
+option java_outer_classname = "UtilProtos";
+
+message ByteArrayList {
+  repeated bytes content = 1;
+}