Add checksum field for the tapplet icons in registry

[MCozhusheck]

Registry should also containg field for icons checksum which would be used by the tari universe to determine if we need to update pre-downloaded icons.

Also consider removing field logoUrl from registry in metadata this field misleading as in case of tariswap-tapplet it's points to src dir which is not present, also it's redundant as registry already holds icons.