Update calc.py

This will allow to correctly calculate line price in basket
Update models.py

We put something in case PriceNotAvailable is raised, maybe we should erase the line.
Update calc.py
Update calc.py
Update calc.py
Update quote.html
Update quote.html
Update quote.html
Update quote.html
Update quote.html
Update quote.html
Update quote.html
Merge pull request #9 from theimip/Basket-fix

Basket fix