Removed pint dependency

[hpohekar]

No description provided.

[seanpearsonuk]

@hpohekar @mkundu1 should we rename quantity.py -> _quantity.py? Should we put a try - except ImportError around import pint in that module and show an appropriate message indicating need to install pint>0.18?

[hpohekar]

@hpohekar @mkundu1 should we rename quantity.py -> _quantity.py? Should we put a try - except ImportError around import pint in that module and show an appropriate message indicating need to install pint>0.18?

Yes, we can rename it to _quantity.py also if needed we can put try-except ImportError because anyhow if pint is not there ultimately it will give standard ModuleNotFoundError as an error message.