Support string or int as argument instead of CV2 flags

[abhisek-lpl]

Currently, many of the augmentations accept cv2 flags as arguments. This is a bit inconvenient because:

1. An extra import of cv2 just for the flags
2. Storing the augmentation configurations in JSoN or any other text-based format is difficult/cumbersome.

It should be easy to bypass this using enum internally and let the methods accept a string or int instead.