Data Pipeline V2: Rename all Output implementations to end in Output

[tchaton]

What does this PR do?

Fixes #937

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[codecov]

Codecov Report

Merging #1011 (d3d750e) into master (b8085f0) will decrease coverage by 8.31%.
The diff coverage is 96.96%.

❗ Current head d3d750e differs from pull request most recent head 779b646. Consider uploading reports for the commit 779b646 to get more accurate results

@@            Coverage Diff             @@
##           master    #1011      +/-   ##
==========================================
- Coverage   82.37%   74.06%   -8.32%     
==========================================
  Files         254      254              
  Lines       13498    13506       +8     
==========================================
- Hits        11119    10003    -1116     
- Misses       2379     3503    +1124     

Flag	Coverage Δ
unittests	74.06% <96.96%> (-8.32%)	⬇️

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

Impacted Files	Coverage Δ
flash/image/detection/output.py	30.00% <50.00%> (ø)
flash/core/classification.py	62.57% <100.00%> (+1.93%)	⬆️
flash/core/data/output.py	83.33% <100.00%> (ø)
flash/image/classification/model.py	70.45% <100.00%> (ø)
flash/image/detection/model.py	68.18% <100.00%> (ø)
flash/image/face_detection/model.py	37.17% <100.00%> (ø)
flash/image/instance_segmentation/model.py	63.33% <100.00%> (ø)
flash/image/keypoint_detection/model.py	68.18% <100.00%> (ø)
flash/image/segmentation/data.py	79.12% <100.00%> (-1.95%)	⬇️
flash/image/segmentation/model.py	91.89% <100.00%> (ø)
... and 46 more

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[ethanwharris]

Looks like some classes are missing from here: https://github.com/PyTorchLightning/lightning-flash/blob/master/flash/core/classification.py

e.g. Labels should become either LabelsOutput or LabelsClassificationOutput

Mind renaming those ones too?

[ethanwharris]

Awesome, LGTM 😃