[SUG][PLAYER] Tile background instead of black bars in menu

[namida]

(See also: Proxima's topic More options for layout customisation, which this was split off from.)

When the player is in windowed mode, or in full screen on a monitor that's not 16:9, black bars are added either to the sides, or above/below, the menu screens to fill the empty space.

A proposal has been put forward to instead, tile the background into this space.

I am not opposed to this, and it should not be too much work. My only concern is that some custom backgrounds may be designed to take up the entire screen and specifically are not suitable for tiling...