Add IconResolver into profiles

[rumkin]

This PR adds new resolver IconResolver which adds an icon property to the resolver. This Icon is a multihash addressing to the icon directory. For example it could be an IPFS CID. The directory should contain a set of icons from size 32px to 512px.

Similar icon format is a standard for native apps developers. Such icons could be used as site/dapp favicon or PWA icon, company logo, personal avatar or other identity.

Discussion

ENS forum: https://discuss.ens.domains/t/iconresolver-proposal/1245

Icon name convention

Grammar:

name
  = "icon_", size, ".png"
  | "icon_", mode, "_", size, ".png"

mode
  = "light" | "dark"

size
  = size-set
  | size-set, "@2x"

size-set
  = "32x32" | "64x64" | "128x128" | "256x256" | "512x512"

Example

Common icon:

icon_32x32.png
...
icon_512x512.png

Light icon example

icon_light_32x32@2x.png
...
icon_light_512x512@2x.png