Mainly docs improvements + small structure and code improvements

[kapi117]

No description provided.

[rayferric]

Please compress the images in docs. Ideally, any media files in our repo should stay under a few hundred KiB, unless it would significantly hurt quality. I can suggest downscaling to lower resolution, attempting to encode as JPEG, or reducing the bit-depth.

I think just one screenshot in kalman_gs would be enough.

Also, those images should be put into ./kalman_gs/docs and ./kalman_arm_controller/docs respectively, so that the packages remain self-contained.