Change type of restrictionCode for uint256

[rya-sge]

See #70

We should reconsider this since :

• Use uint8 instead of uint256 increase the gas cost since EVM works with uint256
• The ERC 1404 is not an official ERC, we don't really need to follow this EIP + we already have divergence with this EIP since we don't implement the ERC-20 interface inside