move methods from OrderData into Order row

- a single place where methods can be overridden
- no getting the cart component class required anymore
add protected method that allows overriding getting price

can be used to implement excl vat prices under special conditions
improve exception message
add variable texts to templates to avoid getting them overwritten in web
fix typo
cache result better, not required to get from apc every time
Merge pull request #43 from vivid-planet/3.3-remove-orderdata

move methods from OrderData into Order row