Hat Image URIs

Like any other NFT, hats have images. The image for a given hat is determined by the following logic:

1. If the hat's imageURI property is set, use that

2. If the hat's imageURI property is not set, then use the imageURI of the hat's admin Hat

3. If the admin hat's imageURI property is not set, then use the imageURI of that hat's admin

4. Repeat (3) until you find an imageURI that is set

5. If no set imageURI is found within the original hat's hat tree (including the Top Hat), then use the globalImageURI set in the Hats Protocol contract

This logic creates flexibility for DAOs to efficiently customize images for their hats, while keeping images as optional and hat creation relatively cheap.