Add --despike option to "imgtool convert"
Add --despike option to "imgtool convert"

Optionally replaces isolated spiky pixel values (i.e., fireflies) with the
median of the 3x3 neighboring pixels.

nyue/pbrt-v3,nispaur/pbrt-v3,nispaur/pbrt-v3,nispaur/pbrt-v3,ambakshi/pbrt-v3,nyue/pbrt-v3,shihchinw/pbrt-v3,shihchinw/pbrt-v3,ambakshi/pbrt-v3,nyue/pbrt-v3,mmp/pbrt-v3,shihchinw/pbrt-v3,nyue/pbrt-v3,nispaur/pbrt-v3,ambakshi/pbrt-v3,mmp/pbrt-v3,mmp/pbrt-v3,shihchinw/pbrt-v3,mmp/pbrt-v3