This introduces a new `popupMenu` property that can be used to pass
down a `StatusPopupMenu` to `StatusChatToolBar`.
The reason this is done is so that we get control over its `onClosed`
handler, which is used to remove the menu button's `highlighted` state.
The `highlighted` state is activated inside the component as well when
it's clicked.
Existing signals like `menuButtonClicked` still exist and can be leveraged
for further logic.
Closes#125
90bad9e312