GUI: List scrollbar actions should focus on list
|Reported by:||salty-horse||Owned by:||sev-|
Since the search box has been introduced to the launcher, it is now possible to move the focus away from the game list.
Clicking on the list's scrollbar buttons or dragging the handle should bring the focus to the list.
Attached is a very hacky patch that implements it. It assumed that a list's boss is always a GUI::Dialog.
Ticket imported from: #2858270. Ticket imported from: feature-requests/554.