add train module and data preparation module

[amirhossein-yousefi]

In this project, I did the following:

1. Adding modules for data preparation for training and writing custom PyTorch dataset class for the CMPFacade dataset so as to iterate through the data efficiently and cleanly.
2. Adding a train module so you can train this model on any custom dataset.
3. In the train module I used gradient accumulation as a feature of PyTorch to train the model instead of explicit batch size. It is great when you don't have a powerful GPU.