[Typo3-shop] price calculations.

[Franz Holzinger]

> Yes, I think only small changes to the tt_products extension will be 
> necessary. Only the price calculation needs an adoption.
> 
And the contract has to be put somehow into the basket.
Maybe a special product should be used to to that. Or the basket should 
be extended that it can use rows from other tables (better solution 
because everything could get bought then)

Franz