Access control for contracts

[ChihChengLiang]

What's wrong

Some of these contracts have no access controls. Which might be a potential attack vector. This issue consolidate those contracts

SpokeRegistry

SpokeRegistry register spoke contracts and maps a spokeID to a spoke contract. Once a spoke is registered, people can send massMigration to migrate their tokens from Hubble to the spoke.

No access control means anyone can register malicious spoke contracts.

tokenRegistry

No access control means anyone can register malicious ERC20 token.

How can we fix it

We don't have governance and we don't want to assign that access to a particular entity.

One way to fix this is to determine all the spokes and the tokens at the deployment and no one are allowed to add new tokens in the future.