Multipe Validation Set Update

[afm215]

• Try to resolve part of How to train it with custom dataset? (webface42m) (folders as classes?_) FileNotFoundError: [Errno 2] No such file or directory: \faces_emore\\agedb_30\\meta\\sizes #109 by introducing a more flexible validation sets code. You should now be able to add .bin files to the existing dataset (the assertion of line 50 in five_validation_dataset is just for consistency purposes, you can remove it if you want to get rid of the initial validation set.
• Edit world size and local rank functions util so that it works with slurm.
• Edit requirements.txt to avoid compatibility error with the code