Fix some bugs and add new feature.

[aimspot]

Update:

1. Create exp in runs;
2. Create balance plot;
3. Acceleration of processing

Add:

1. New classes txt file;
2. New api _example.ipynb;

Fix:

1. Fixed errors when using the val folder instead of valid;
2. Fixed errors when creating a config for the ssd model that caused the gradient to zero;
3. Automatic resizing of images and annotations has been added for ssd 300.
4. The code for obtaining paths for the dataset has been optimized, now you can simply specify the name of the dataset or the path to it, if the dataset is not in users_dataset, it will be copied there;
5. Fixed errors during split dataset, now you can not specify the size of the test sample, it will be collected from the remaining images and annotations;
6. Fixed some bugs with paths
7. Ml model split data

Delete:

1. Folder yolo in user_dataset;
2. File prepare_train