mod_http_oauth2: Tweak method of centering the UI The percentage here was relative to the viewport width, which on some very wide screens may put the UI slightly outside of the view, requiring scrolling to see. By using a unit relative to the height of the viewport, this is avoided and should work better. But no guarantees, it's still possible to resize the browser or adjust font sizes so that the UI goes out of view.

Over the years, some servers stop working for various reasons, and leave
behind broken roster subscriptions that trigger failing s2s connections.
This module allows cleaning up such cases by unsubscribing local users
from their contacts on those servers. Also works for typos and the like.
Use with care.

```lua
Component "gmail.com" "unsubscriber"
```