VISSL initial integration

[ananyahjha93]

What does this PR do?

POC PR for VISSL

Fixes # (issue)

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[codecov]

Codecov Report

Merging #682 (4f68899) into master (d963de7) will increase coverage by 0.54%.
The diff coverage is 80.18%.

@@            Coverage Diff             @@
##           master     #682      +/-   ##
==========================================
+ Coverage   89.07%   89.62%   +0.54%     
==========================================
  Files         198      213      +15     
  Lines       10693    11317     +624     
==========================================
+ Hits         9525    10143     +618     
- Misses       1168     1174       +6     

Flag	Coverage Δ
unittests	89.62% <80.18%> (+0.54%)	⬆️

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

Impacted Files	Coverage Δ
flash/audio/classification/cli.py	100.00% <ø> (ø)
flash/audio/speech_recognition/cli.py	100.00% <ø> (ø)
flash/graph/classification/cli.py	92.30% <ø> (+49.45%)	⬆️
flash/image/classification/cli.py	84.61% <ø> (-1.10%)	⬇️
flash/image/classification/data.py	94.11% <ø> (ø)
flash/image/detection/cli.py	100.00% <ø> (ø)
flash/image/detection/data.py	93.75% <ø> (ø)
...lash/image/embedding/vissl/transforms/multicrop.py	96.96% <ø> (ø)
flash/image/instance_segmentation/cli.py	100.00% <ø> (ø)
flash/image/instance_segmentation/data.py	88.23% <ø> (ø)
... and 81 more

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[ethanwharris]

LGTM! Docs, docstrings etc. to come in follow-up 😃

[ananyahjha93]

@ethanwharris The image classification notebook is failing when loading the checkpoint from s3.

[tchaton]

Great work ! Definitely looks much better now :) Still some comment, but can be addressed in the following PR.

[tchaton]

some docstrings would be good. Same below.