Libellus Potionis 0.83.0

Fixed: importing a backup with "Replace" now really replaces the drink list — the built-in preset drinks are no longer kept alongside the imported ones. Fixed: the Statistics and Calendar cards now have the same background as the rest of the app. The language list now offers "(System)", so a fixed language can be switched back to following the device language. And the overflow menu's About screen shows the version, the GPL notice and the licenses of the app's components.