Display material for project tips

• feature.png (4:3) , icon.png (1:1) , cover.png (1:1) files can be added directly to the collection folder.

• If no display material is provided, the website will use the zero HASH as the parameter to generate the material after the collection is launched.

let zeroHash = '0x0000000000000000000000000000000000000000000000000000000000000000'