Make items compatible with EIP-721

[greenlucid]

This would allow explorers such as Etherscan to show that these items exist.
There's no need to implement a tokenURI, as that would introduce edge cases. But, a general one could be made, or maybe a general one per list.
Probably, it would need to implement ERC-721 Enumerable, along with other stuff.
Since Stake Curate takes place in a rollup, the extra gas overhead may not be significant, as long as the EIP-721 doesn't leak into creating more calldata for the transactions.
The L2 gas will increase a lot, as now it would need to keep track of extra information such as how many items are owned per user.

The transfer functions will probably need to be reverted, as owning items is a liability.

[greenlucid]

I decided against this:

• Etherscan and other explorers often require extra metadata to render the NFTs
• Increases gas with the new events, methods, and extra regular storage writes needed.
• Bytecode would most definitely go over the 24 kB limit
• Increases complexity significantly, which is already barely manageable
• balanceOf (from Enumerable EIP-721) would not be technically correct, as it is not possible to read how many items an account has included.