protob: Change some Lisk transaction fields to `bytes`

protob/types.proto

@@ -479,9 +479,9 @@ message LiskTransactionCommon {
 	optional uint64 amount = 2 [default=0];
 	optional uint64 fee = 3;
 	optional string recipient_id = 4;
-	optional string sender_public_key = 5;
+	optional bytes sender_public_key = 5;
-	optional string requester_public_key = 6;
+	optional bytes requester_public_key = 6;
-	optional string signature = 7;
+	optional bytes signature = 7;
 	optional uint32 timestamp = 8;
 	optional LiskTransactionAsset asset = 9;
 }