Allow ordering and labeling screens on X11

[DASPRiD]

Currently screens are displayed in their port order on X11, which does not necessarily match their real order. It'd be great if there was a config (file) option to define their order, and potentially also give the screens custom labels.

[galister]

There is no standard to screen names in xorg, some DEs expose the connector name (DP-2), some expose the number (Screen 1), some don't expose a name at all.

All we have is the 0-based index of the screen, which will change when you plug in a new screen or unplug an existing one, breaking any index-based mapping.

[DASPRiD]

Would it be possible to sort by the screen position, since we do have the offsets?