Add new functionality - retrieve cart / remove item

[felix63]

Hi Mike,

It would be lovely if you could add functionality to retrieve the current content of the shopping cart to a sensor. Then I could use https://github.com/iantrich/list-card or similar to list the current content of the cart. When that happens I'll start asking about options to delete items from the shopping cart ;-)

Love what you've done so far!

Regards,
Lex