[intro_supply_demand] Adding to supply and demand lecture (#372)

* Adding to supply and demand lecture

* misc

* @mmcky vscode review

* @mmcky review in jupyter lab, standardise colors + math updates

* migrate to namedtuple over class implementation for Market

* add links and references to pyprog:scipy

* update explantion text for create_market function

* @mmcky re-read

* fig: add captions and numbers

* fix config status issue

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Co-authored-by: mmcky <mamckay@gmail.com>