Add "Standard" tax class about woocommerce-product-fees HOT 2 CLOSED

Standard tax class was deliberately removed in commit 2203f42](2203f42), because it was not working properly.

Why Standard Tax Rate doesn't work

There is a design flaw in how the "Fees Tax" option was handled. The "don't apply tax" option is given a tax class ID equal to an empty string. Such ID is already reserved by WooCommerce, for the Standard Rates (in the plugin it was assumed, incorrectly, that the Standard tax class had the "standard" ID).
The same issue affects the tax calculation: when the tax class ID is empty, the plugin assumes that no tax should be applied, while the Standard rate should be used instead.

How to fix the issue

I prepared a patch that handles tax rates correctly. Pull request coming shortly.

from woocommerce-product-fees.

Fixed here d49ea61

And added additional feature here: d49ea61

from woocommerce-product-fees.