Calculating item price via details page is incorrect

[MaX-Lo]

If a item has no price we try to get that price via the details page by simply looking for the string behind "Summe:". This results in:

• not checking for discounts which are subtracted afterwards
• setting the full order price for a item when having multiple items in an order is very wrong
• setting the price as string instead of float is inconsistent with normal prices being floats