Global model supporting functions

[jejarosl]

Description

Adding the CNN Image Retrieval model implementation based on the following papers:

[1] Fine-tuning CNN Image Retrieval with No Human Annotation,
Radenović F., Tolias G., Chum O., TPAMI 2018 [arXiv]
https://arxiv.org/abs/1711.02512

[2] CNN Image Retrieval Learns from BoW: Unsupervised Fine-Tuning with Hard
Examples, Radenović F., Tolias G., Chum O., ECCV 2016 [arXiv]
https://arxiv.org/abs/1604.02426

Type of change

• New feature (non-breaking change which adds functionality)
• A new research paper code implementation

[andrefaraujo]

Thanks Kate! Please take a look at the comments :)

[andrefaraujo]

Thanks for the new commit Kate! I saw a couple more minor code style issues, see new comments.

Regarding the function that applies whitening, it would be great if we could consolidate / avoid duplication with the other one I mentioned. LMK if that ends up being possible :)

[andrefaraujo]

Thanks Kate, looks great!