use PBO for timelapse data read

src/app.h

@@ -96,7 +96,7 @@ public:
     int rec_count = 0;
     std::mutex rec_mutex;
     std::condition_variable rec_cv;
-    std::deque<std::unique_ptr<Image>> rec_frames;
+    std::deque<std::unique_ptr<PBO>> rec_frames;
 
     RTT uirtt;
     Sampler sampler;