Release v4.73.0

Changed

• An application's own root template that fills a slot itself (for example a storefront's topbar) now says what is drawn there: the host's default chrome only seeds the slots the template leaves empty. A blueprint root template's content stays placeholder seed that the host's chrome replaces.
• New bar component of the default blueprint: a horizontal bar for an application's own shell (start brand, center - or the topbar navigation region when empty -, end actions), needing no sidebar or layout configuration.
• New indicatorButton component: an icon button with a live count badge (icon, label, count) said in words as well as in the badge; the count is a query result and pressing it runs the attached behaviors. New cart and bell foundation icons.

Fixed

• An own root template's content topbar was replaced by the host's default topbar. (#217)