ERC1155: Change access control for Interfece-based methods.

[mrklos]

Fix for #461

[JeneaVranceanu]

@mrklos Looks good.

I thought about making protocols public but after reading some meta-questions on SO changed my view to:

We provide implementations of ERC standards and do not expect people to use protocols to implement them by themselves.

But! 🤔
As the number of protocols grows in web3 space and they are mostly built on top of some old protocol the question of making protocol IERC... public becomes more reasonable.

But it's definitely not a priority right now.

[JeneaVranceanu]

@mrklos Since we provide implementation could you run through all of the ERCXYZ classes to make sure functions that are implemented as protocols requirements are marked public?

Anyway, anyone can access methods that these functions call if developers use "low-level approach" of calling functions via contract.read or contract.write. It's not something private from the smart contract perspective.