Weird infobar after ending call

Running master on my Birch phone with the dummy backend I'm currently seeing this:

1. Dial a number
2. Initiate call
3. End call by tapping the red button
4. Dialer opens
5. An odd infobar saying "Disconnected" appears at the top of the screen

We should not show this infobar in this case, because it looks like an error when there wasn't any (I just ended the call normally).

If this same infobar is used for other scenarios (e.g. if something actually goes wrong) we can keep it for those cases, but I'd make the following style changes:

• Style it like an in-app notification (OSD styling, centered rather than full-width)
• Fix the odd vertical alignment (there's more margin at the top than at the bottom)
• Use more descriptive labels ("Disconnected" isn't very helpful, it would be better to state what, if anything, went wrong)