Image classification csv data source

[ethanwharris]

What does this PR do?

Fixes #257

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[codecov]

Codecov Report

Merging #556 (6ce1679) into master (fb51cc4) will increase coverage by 0.02%.
The diff coverage is 94.11%.

@@            Coverage Diff             @@
##           master     #556      +/-   ##
==========================================
+ Coverage   91.31%   91.33%   +0.02%     
==========================================
  Files         112      112              
  Lines        7128     7193      +65     
==========================================
+ Hits         6509     6570      +61     
- Misses        619      623       +4     

Flag	Coverage Δ
unittests	91.33% <94.11%> (+0.02%)	⬆️

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

Impacted Files	Coverage Δ
flash/image/classification/model.py	86.66% <ø> (ø)
flash/image/classification/data.py	94.66% <94.11%> (-0.63%)	⬇️

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[ethanwharris]

@aniketmaurya Mind reviewing this? I can't request a review from people outside PL org I think

[aniketmaurya]

Looks good! Thanks for adding this feature @ethanwharris 🚀