Support basic token metadata

Zeto tokens should have some limited ability to identify themselves with basic metadata - at the very least, it seems useful to have a "name" as part of the constructor.

We could also opt to align with [ERC20](https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/extensions/IERC20Metadata.sol) and provide `name`, `symbol`, `decimals`.