Migrate to Python 3

[MaxGyver83]

Changes:

• Update shebang line
• Replace print statements with print() functions
• Import tkinter instead of Tkinter
• Import tkinter.filedialog instead of tkFileDialog
• Image.ANTIALIAS was renamed to Image.LANCZOS

[pknowles]

Thanks very much for taking the time to do this. I think I've merged your and the other open PRs into a new main now. FYI I'm experimenting with a few updates in https://github.com/pknowles/cropall/tree/use_pyinstaller but I don't have a lot of time spare.