[WIP] crestereo draft implementation

[TeodorPoncu]

This is a draft version for the CREStereo model implementation.

It's over-commented for easier readability for those that are unfamiliar with the paper.

It also makes use of ModuleDicts and Dicts to process / access feature pyramid level instead of ModuleLists and Lists for readability purposes.

[jdsgomes]

you also need to add from .crestereo import * to torchvision/prototype/models/depth/stereo/__init__.py

[YosuaMichael]

@TeodorPoncu Oh ya, also please resolve the conflict on the test files