StockRecord: rename price_excl_tax

The docstring for price_excl_tax already explains what it truly is: the base price for tax calculations. I’ve had two projects where we knew the tax-inclusive price, and only calculated the price excl tax. I’d argue that a stock record is merely a record of a base price, and only the pricing policy gives it any meaning in regards to tax, so the field name should reflect that. I realize that the field is probably used directly more often than it should (instead of through pricing strategies), so we need a good idea about being friendly as far as backwards-compatibility is concerned.

[sasha0]

After research and observation, I came to conclusion it does make sense to rename price_excl_tax into price but as @john-parton mentioned before, there’s no chance to make this change backwards compatible which drastically reduces motivation to apply this change.

I also totally agree with @maerteijn that we’d firstly deprecate this field and rename in the next major release (2.0).

[solarissmoke]

We forgot about the renaming of price_excl_tax - will definitely do this before the next release.