The themed launcher icon shows its lettering again: RETE over KEY,
punched through the key caps so the theme's own background shows in the
shape of the letters - the themed-icon equivalent of dark ink on a pale
cap, and what the ordinary icon has always shown.

The layer is a bitmap now, one per density, because a vector drawable
cannot subtract a stroke from a fill and rebuilding the letters as
polygons left a speck at every joint. One raster composite punches them
out cleanly, which is also how reteclock ships its themed icon.
