Updated train_test_split.py

[CatcherInThePy]

• The previous version worked only for ".jpg" files. This version can work for all file extensions in images directory. The image extensions can also be mixed.
• The output now separates txt files and images. The output directory can directly be used with yolov5.
• The new version can also take optional arguments namely:
  • Custom dataset directory name
  • Test split size
  • Images directory path
  • Bounding box txt files directory path