ACC Cost: document templates: make the tax "base amount" available as a variable

[johan_van_mol]

When creating document templates in ACC Cost, you can only access these variables related to taxes:

• Amount
• Name
• Rate
• Type

Imagine 21% tax has to be paid on an item that costs $1.000,00:

• Amount = $1.000,00 * 21% = $210
• Name = "21% tax"
• Rate = 21
• Type = ?

In Belgium, we also need to know the "Base amount" on which a tax was calculated.

You can manually calculate the "Base amount":

Base amount = Amount / (Rate/100)

For example: 

1.000,00 = 210 / (21/100)

The problem is that we sometimes need to use a 0% tax rate.
In that case, the Base amount can't be calculated, because it would require dividing by zero.