Add prediction unwrapping and serialization for icevision tasks

[ethanwharris]

What does this PR do?

Fixes #639

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[codecov]

Codecov Report

Merging #727 (db70df5) into master (4ebc45d) will decrease coverage by 0.02%.
The diff coverage is 81.52%.

@@            Coverage Diff             @@
##           master     #727      +/-   ##
==========================================
- Coverage   89.38%   89.36%   -0.03%     
==========================================
  Files         197      198       +1     
  Lines       10517    10538      +21     
==========================================
+ Hits         9401     9417      +16     
- Misses       1116     1121       +5     

Flag	Coverage Δ
unittests	89.36% <81.52%> (-0.03%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
flash/pointcloud/detection/open3d_ml/app.py	26.59% <ø> (-0.78%)	⬇️
flash/pointcloud/segmentation/open3d_ml/app.py	33.33% <ø> (ø)
flash/core/integrations/icevision/data.py	86.27% <68.18%> (-9.56%)	⬇️
flash/core/integrations/icevision/transforms.py	72.50% <77.50%> (+3.05%)	⬆️
flash/core/integrations/icevision/adapter.py	93.05% <87.50%> (+0.09%)	⬆️
flash/core/data/batch.py	95.93% <100.00%> (-0.59%)	⬇️
flash/core/data/serialization.py	100.00% <100.00%> (ø)
flash/image/detection/data.py	93.75% <100.00%> (ø)
flash/image/detection/model.py	100.00% <100.00%> (ø)
flash/image/detection/serialization.py	93.87% <100.00%> (+3.49%)	⬆️
... and 7 more

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[tchaton]

Awesome !