Block ERC721 transfers

[rotcivegaf]

Block the transfers of ERC721:

• transferFrom(address,address,uint256)
• safeTransferFrom(address,address,uint256)
• safeTransferFrom(address,address,uint256,bytes)

Use _transfer instead of transferFrom

And add transfer test

[TimDaub]

Hey thanks for your work here, I really appreciate it. I originally planned to make a bigger change on the main branch but then focused on something else. Anyways, my original plan had included using https://github.com/attestate/ERC5192 as this would then also encapsulate the blocking and its details in that standard. The plan was also to make the changes to the specification in that regard. Would you be up to do that? I‘m happy to assist!