Center scroll lists when navigating with keyboard
Center scroll lists when navigating with keyboard

- This applies to channel list and user list sidebars
- This avoids having a selected item behind a sticky header
- This provides better UX by starting the scroll before the bottom (or top) is reached, giving a preview of what comes next (or before)

MaxLeiter/lounge,FryDay/lounge,williamboman/lounge,ScoutLink/lounge,williamboman/lounge,FryDay/lounge,thelounge/lounge,williamboman/lounge,MaxLeiter/lounge,ScoutLink/lounge,FryDay/lounge,ScoutLink/lounge,MaxLeiter/lounge,thelounge/lounge