Refactor: use PIL as default image format

[Borda]

What does this PR do?

follow-up to #1313 as the Tensor formating is not very friendly to other general augmentation packages

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• Did you write any new necessary tests? [not needed for typos/docs]
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PR review

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[krshrimali]

Part-1 of my review. I'll appreciate it if you can briefly explain why this was required, and what was the problem before (it will be easier to review and land if all looks good). :)

[ethanwharris]

Awesome! Few comments. Let's merge this before updating #1313 so that it can work directly with the PIL image

[krshrimali]

Hi, @Borda - Would you mind adding tests to this PR? Just a sample test will work, even if it fails, I'll take it from there. Thanks!

[krshrimali]

Hi, @Borda - Would you mind adding tests to this PR? Just a sample test will work, even if it fails, I'll take it from there. Thanks!

Hi, @Borda - Just a gentle ping, if you can write a test (as I mentioned before - no need to ensure that it passes, just a template test that helps me understand what you are trying to achieve here will help) - that will be great! Please ping me once you are done, also don't worry about the merge conflicts. I'll take care of it, just force push the test. :)

[Borda]

@krshrimali @ethanwharris may pls get your help on this collision resolution... 🐰

[codecov]

Codecov Report

Merging #1319 (4eea743) into master (f26e3df) will decrease coverage by 6.01%.
The diff coverage is 96.29%.

@@            Coverage Diff             @@
##           master    #1319      +/-   ##
==========================================
- Coverage   92.29%   86.28%   -6.02%     
==========================================
  Files         287      287              
  Lines       13056    13047       -9     
==========================================
- Hits        12050    11257     -793     
- Misses       1006     1790     +784     

Flag	Coverage Δ
pytest	13.30% <0.00%> (+<0.01%)	⬆️
tpu	13.30% <0.00%> (+<0.01%)	⬆️
unittests	86.78% <96.29%> (-6.06%)	⬇️

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

Impacted Files	Coverage Δ
flash/core/data/transforms.py	94.73% <ø> (-1.76%)	⬇️
flash/image/segmentation/input.py	82.71% <92.30%> (-17.29%)	⬇️
flash/image/data.py	100.00% <100.00%> (ø)
flash/image/segmentation/input_transform.py	95.55% <100.00%> (+0.96%)	⬆️
flash/image/segmentation/model.py	94.04% <100.00%> (ø)
flash/image/segmentation/viz.py	89.83% <100.00%> (+1.89%)	⬆️
...lash/image/embedding/vissl/transforms/utilities.py	15.15% <0.00%> (-84.85%)	⬇️
flash/image/embedding/heads/vissl_heads.py	35.29% <0.00%> (-64.71%)	⬇️
flash/image/embedding/losses/vissl_losses.py	37.50% <0.00%> (-62.50%)	⬇️
flash/image/embedding/vissl/adapter.py	31.63% <0.00%> (-62.25%)	⬇️
... and 42 more

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