Cleanup fetch_file_cached() operations in the download model

[Arkay92]

Old data was being left behind using os.rename. By switching to shutil we can move the file and delete the old cache data so temp files are properly cleaned up.

[dancergraham]

Hello,

shutil is part of the standard library so it should not be added to setup.py

[Arkay92]

My bad good spot graham will undo with a new commit

[dancergraham]

You're very welcome ! Also on a point of personal preference I would remove code comments which say what the code is doing - that should be clear from the code. I think comments should explain why and the code itself should be clear. For instance the comment below is not needed because the code itself is very clear:

    # Return local path
    return local_path