Export overlay with map

Being able to use the overlay as a background/foreground (using the already existing transparency) could be nice.
Currently using a abstract plane only works for squared assets (or editing the asset to have transparent edges to make it square)
A more controllable abstract could fit the bill as well (adjustable width/length)
This could also be useful to quickly add a grid to an existing map (creating a new map, setting the overlay/asbtract and adding the grid on export)