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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• [x] Was this discussed/approved via a Github issue? (no need for typos and docs improvements)
• [x] Did you read the contributor guideline, Pull Request section?
• [x] Did you make sure your PR does only one thing, instead of bundling different changes together?
• [ ] Did you make sure to update the documentation with your changes?
• [ ] Did you write any new necessary tests? [not needed for typos/docs]
• [ ] Did you verify new and existing tests pass locally with your changes?
• [ ] If you made a notable change (that affects users), did you update the CHANGELOG?

PR review

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Make sure you had fun coding 🙃

[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... :rabbit:

[codecov[bot]]

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%)	:arrow_up:
tpu	13.30% <0.00%> (+<0.01%)	:arrow_up:
unittests	86.78% <96.29%> (-6.06%)	:arrow_down:

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

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