Instead of storing price ex. vat, we use the catalog settings. This
eliminates rounding errors and needing to store totals to high
precision.
Also, now storing tax class/status, line cost, and line tax. This will
allow us to support compound and stacked taxes (which are too complex
to do by storing just tax rate alone).
Old orders data will be missing for line item costs, but order totals
will be unaffected. This is unavoidable.
This is so they are hidden (_). Should have done this long ago. Few
extensions will need updating when 1.4 goes out to reflect these
changes, mainly importers.