Enhance stereo depth

[alex-luxonis]

Add options to configure:

• the kernel size of the median filter that is applied over the disparity map: 3x3, 5x5, 7x7 (default), or disabled.
• enabling the Left-Right check feature (runs disparity on both directions and combines them).

  -med {0,3,5,7}, --stereo_median_size {0,3,5,7}
                        Disparity / depth median filter kernel size (N x N) .
                        0 = filtering disabled. Default: 7
  -lrc, --stereo_lr_check
                        Enable stereo 'Left-Right check' feature.

Currently, the disparity map works well (disparity, disparity_color streams), but there is a problem with depth_raw and the -lrc option (WIP).
(It's also better to use a disparity stream to visualize the map quality).

Currently, with -lrc, the median filtering (if not disabled) is applied on each direction (L-R and R-L), before combining. We may need to move it after the combine step.

Example usage: ./depthai.py -s disparity_color -med 5 -lrc

[alex-luxonis]

Merged in the branch metadata_disparity_depth, with these changes:

• added frame metadata for disparity, disparity_color, depth_raw streams too. Previously it was present only for previewout, left, right, metaout (NN packets).
• fixed streaming out depth_raw with the full resolution 1280×800 (-monor 800 option)

[VanDavv]

@alex-luxonis can we close this PR? I tried to also check metadata_disparity_depth but there seems to be no -lrc or med flags.

Currently, this branch produces a flickering result

[alex-luxonis]

Will rebase the work here on develop, then close it. The flicker should only happen with -lrc which is a new option (and I'll fix it).
About the metadata_disparity_depth branch, that one was merged into this. So now metadata_disparity_depth is obsolete.

[Luxonis-Brandon]

I think we can close this now. So closing now but we can always reopen.