[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)