Expose the VAT amount of an expense receipt (ExpenseClaimDetailDto)

[Véronique]

The VAT amount was exposed in ExpenseReceiptDto after we requested it.

It turns out that our app would be much faster if the taxTotal was also exposed in ExpenseClaimDetailDto.

We get a list of expense claims (which necessarily contain a list of ExpenseClaimDetailDto) before we display the list of receipts, therefore we would spare quite a few API calls if the taxTotal was already available in this model.