Create strategy for OpenZeppelin ERC20Votes with individual override option

[serenae-fansubs]

This strategy is similar to ERC-20 Votes, except that it also allows individual delegators to override their vote on a particular proposal if they wish. This is most useful for social (off-chain only) proposals.

If an account has any delegated voting power returned from getVotes, adds that value, minus the balances from any delegators that have also individually voted.

If an account is delegating to itself, then its own token balance will already be included in the getVotes return value.

If an account is delegating to a different valid address, adds the local token balance. The account must be delegated to another valid address, otherwise the local token balance will not be added.

Primarily for token contracts using OpenZeppelin's ERC20Votes: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/extensions/ERC20Votes.sol

However the getVotes method can also be overridden in the options too if need be.