[flint] Improve flint image

This MR fixes issues relative to images

• Download images based on preferred user refresh rate
  • Tested with 1000 images at 100Hz
  • Previously 1000 images was downloaded
  • Now about 40 with refresh rate at 500ms
  • Should reduce network and CPU load, but did not notice a huge change on the CPU side
• Display image source in the GUI (can be video, file, memory: memory buffer of the camera)
• Display almost equal (≈) frame id for the video (right now Lima do not provide a video frame id = image id)