index.html.in: two transition fixes

index.html.in: two transition fixes

First, the repositioning of the ticket also needs to be transitioned.
This makes the QR animation much smoother.

Second, it would seem that appending the "loaded" class (to enable
transitions) can retroactively affect style changes that were made
before the class was appended. The workaround for this is to do
something that makes the browser re-flow the affected elements, and I
guess calling focus() suffices to do that. So we add in a call to
focus() before appending the "loaded" class to the ticket and its
background; this ensures that the transitions are not enabled until
after the initial ticket sizing, as was always the intent.