Change Purchase Taxes and Charges default field for category to 'Total'

[tundebabzy]

Inspired from #11845
Most taxes that will go into a purchase invoice will mostly be recoverable taxes which should not be added to the Item's valuation. The default for category under Purchase Taxes and Charges is "Valuation and Total". This PR changes it to "Total" for user convenience.

[GSLabIt]

I think would be better to differentiate Taxes from Charges, as all Charges like shipping, logistic cost has to be added to valuation while taxes are recoverable so, as discussed, haven't to be included in valuation.

Other than that charges would be per item and per supplier, as different supplier could add different charges.