Fixed some errors in Zakup and ListaZakupow.
Added an API for posting ListaZakupow.
Fixed missing error messages in some forms.
Adjust Klient and Pojazd details depending on whether they are for a new or an existing instance.
Moved splashscreen into a separate file.
Added a function to get ListyZakupow for all Dostawcy.
Added textual counter to Czesc progress bar.
Added ListaZakupow editor.
Fixed security rules for mailing (un)subscribing.
Some fixes and appearance tweaks for the Faktura editor.
Implemented row adding and deleting in the Faktura editor.
Implemented automatic net/gross calculation in the Faktura editor.
Tweaked Faktura generation workflow.
Adapted Faktura to the new database scheme and improved the appearance.