Add protobuf syntax version

The protocol buffer spec suggests that this is required.
I've tried two protobuf libraries, and one errors without this,
and the other prints a warning.

There's no documentation in OLA I can find that it's proto2,
but it works this way, and it makes sense.  Both files use "required",
which was removed from proto3.

Author: Ken Harris

common/protocol/Ola.proto

@@ -18,6 +18,8 @@
  * Copyright (C) 2005 Simon Newton
  */
 
+syntax = "proto2";
+
 package ola.proto;
 
 option cc_generic_services = false;

common/rpc/Rpc.proto

@@ -18,6 +18,8 @@
  * Copyright (C) 2005 Simon Newton
  */
 
+syntax = "proto2";
+
 /*
  * Based on, but not guaranteed to be the same as the specification here:
  * http://protorpc.likbilen.com/Protorpcdocprotobuf.html