schema: Bump animation duration to 400ms

167ms is way too short for new gtk animations.
app-window: Add a 'connecting' page

Show a spinner in the middle of the view and hide items between the time
user clicks on the item and we get to show the display.
topbar: Remove now redundant spinner

Now that we show spinner in the middle when connecting to a box, we
don't need the small spinner on the topbar. It was pretty easy to miss
anyway.