[inequality] Update lecture to include Lorenz Curve (as a function) rather than from quantecon package

[mmcky]

It was discussed that we should write a Lorenz curve function locally to show what the function is doing and to assist with enabling this lecture series to be wasm compatible.

• write Lorenz Curve function in the lecture without the use of numba (reported to QuantEcon.py as well Fix numba deprecation notice QuantEcon.py#721) to show students what that function does.

For reference the code can be found here

https://github.com/QuantEcon/QuantEcon.py/blob/d7c2f5261301ff159c32dd79300e500a442856bc/quantecon/_inequality.py#L11