Feature: Unread counter in View Switcher

So, it was brought up by Cawbird-dev @IBBoard inside an Issue in Cawbird if it would be possible to add an "Unread"-Counter in the ViewSwitcher. After a little bit of discussion with @exalm we found that it would be best to request it upstream.

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Requested Feature

Adding a "Unread Items" counter to HdyViewSwitcher. This requires an additional property in GtkStack, so we would need to fork it as HdyStack.

Changes to be made

• Fork GtkStack as HdyStack and add "Unread Items" property.
• Adding a label to HdyViewSwitcherButton to display the new property.

Possible Usecases

• Cawbird: Display unread tweets in home or mentions timeline
• Software: Display updates to be done
• Calls or Chatty: Display missed calls/unread messages when in other view (such as contacts).

Possible Design

Also mentioning @bertob for comment on design.