Move fps counter out of video buffer

In order to make video buffer more generic, move out its specific
responsibility to count the fps between the decoder and the renderer.

app/src/input_manager.h

@@ -16,6 +16,7 @@
 struct input_manager {
     struct controller *controller;
     struct video_buffer *video_buffer;
+    struct fps_counter *fps_counter;
     struct screen *screen;
 
     // SDL reports repeated events as a boolean, but Android expects the actual