TODO:

Refactor:

Testing:
- write tests for strops.hpp
- write tests that check error handling for corrupt files. (e.g. references to tax rates, project and cost center that failed to load)

Improvements:
- Load all tax rates from all countries into new list, should be loaded before a file is imported. We can get rid of invoice_recalculate_totals after this.
- AI importer: query questions in batches and fill template in code
- AI importer: all address data should be editable because import is not perfect
- AI importer: file path should not be editable as it is imported
- AI importer: real error logging for OpenAI and importing in general
- AI importer: log elapsed time for ai requests

Features:
- Handle invalid api key response from AI backends and display in settings UI
- error log for tax report to display invoices not yet supported for tax generation or invoices with invalid tax rates
- minimum invoice date for tax report generation, show warnings for unsupported invoices
- create invoice PDF for NL https://goedestartbelastingdienst.nl/wiki/view/50bdccd8-f9a0-4297-b57f-3a6651cbe05c/factuureisen
- toggle on invoice form wether price is inclusive of tax.
- retrieve available balance from AI api & show in settings/services.
- Send invoice by email
- create invoice from image of receipt
- create invoice from UBL file
- read invoice from Holodeck instance
- send invoice via Holodeck instance
- View invoice history for contacts
- View invoice history for projects 
- validate data within administration on save to make sure it is valid for transmissions. (e.g. rules of https://docs.peppol.eu/poacc/billing/3.0/syntax/ubl-invoice/cac-AccountingSupplierParty/cac-Party/cbc-EndpointID/)
- View local business number / vat number naming on contact form. e.g. when country is austria: "Österreichische Umsatzsteuer-Identifikationsnummer"
- ICP reports