Re-add Missing Modules

[voetberg]

There are some missing modules that would make it impossible to run this code.

Ones documented are:

• LinearAverage in models
• mydataset and ImageFolder
• UnalignedDataLoader
• Inference (in general)

[AleksCipri]

I found a missing loss function. So that is added. I'll try to figure out the rest...but I doubt that I'll be able to resolve all of this without Ashia :(

[AleksCipri]

Also added models/LineareAverage.py from Wu et al 2018.
https://github.com/zhirongw/lemniscate.pytorch/blob/master/lib/LinearAverage.py

[AleksCipri]

ImageFolder and UnalignedDataLoader I found here:
https://github.com/zhengqili/unsupervised-learning-intrinsic-images

I hope nothing is modified compared to the original code, but I feel that at least ImageFolder is likely modified in some way...