Dev/feature yolo

[bamsumit]

Issue Number: 242

Objective of pull request:
YOLO SDNN training and GPU inference pipeline

Pull request checklist

Your PR fulfills the following requirements:

• Issue created that explains the change and why it's needed
• Tests are part of the PR (for bug fixes / features)
• Docs reviewed and added / updated if needed (for bug fixes / features)
• PR conforms to Coding Conventions
• PR applys BSD 3-clause or LGPL2.1+ Licenses to all code files
• Lint (flakeheaven lint src/lava tests/) and (bandit -r src/lava/.) pass locally
• Build tests (pytest) passes locally

Pull request type

Please check your PR type:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation changes
• Other (please describe):

Does this introduce a breaking change?

• Yes
• No

Supplemental information

[bamsumit]

Dear Reviewers,

Do not fret seeing a lot of files in the PR. Here are the main files to be reviewed in the order of priority. Please :

• tutorials/lava/lib/dl/slayer/tiny_yolo_sdnn/README.md
• tutorials/lava/lib/dl/slayer/tiny_yolo_sdnn/train_sdnn.py
• tutorials/lava/lib/dl/slayer/tiny_yolo_sdnn/inference.ipynb
• src/lava/lib/dl/slayer/object_detection/models/tiny_yolov3_str.py
• src/lava/lib/dl/slayer/object_detection/models/yolo_kp.py
• src/lava/lib/dl/slayer/object_detection/boundingbox/metrics.py
• src/lava/lib/dl/slayer/object_detection/boundingbox/utils.py
• src/lava/lib/dl/slayer/object_detection/dataset/bdd100k.py
• src/lava/lib/dl/slayer/loss.py
• and the rest :)

[mgkwill]

A few places to remove commented code and a couple of comment spelling errors, else LGTM.