Generate icon shadow

[otomad]

The new start menu for Windows 10 2004/20H2 is coming. And the new Fluent Design icons which were recommended by Microsoft, usually have a shadow under the icons. Then the tile will be better-looking. So I suggest that it can be added a new feature to generate shadow under the normal icons easily.

Else, it is hard to control the size of the icons. I suggest put the auxiliary line on two tile which are used for preview. Then it will be easier to unify the size of all icons.