Add a symbol sprite for Quality Transfer mode

Currently, (hr-)selector-displays.png contains five sprites, and all are used by other modes (`Select input` mode uses two). Extend this with a sixth sprite to indicate Quality Transfer mode.

Start with (hr-)selector-displays.png and inspect the five existing sprites and how other modes, including Select input, reference them. Add a sixth sprite for Quality Transfer mode, preserving the existing sprite usage and layout; done means the new mode has a distinct symbol available in that image.

Written by the indexing model from the issue text.