Draft: Flint: Dynamic density filter for images

This MR added add an optional filter to the image display.

From a @wright feedback; with the help of @tvincent

This filter using density map on the displayed image (with a max filter). It is updated dynamically to the current zoom used in the plot.

The 2D bins are computed using a nearest step which is fast but will create artefacts in the resulted image. A slowest but accurate filter could be added later.

@wright if you think it can already be useful for your beamline, let me know and we can try to hotfix Flint. I think it is easy to backport to your BLISS version.

Other filters like that could be added, like 65535 removal.

Here is a result with a noisy image, and it allows to see the location of all the peaks (which are probably masked pixels here).