Detector: Improve simple detector logic

[mbelluzzo]

The way it is know is practically useless even for sense + stop. The drone will always stop because of the camera input noise. We should change the filter to detect some blobs instead of solely rely on single pixels of the depth map. Also very short distances needs to be filtered based on Depth Camera limitations.

[mbelluzzo]

It became an code example, it doesn't matter anymore.