Multisig solidity wallet

MultiCat.sol

pragma solidity ^0.4.18;
contract ERC721 {
    function totalSupply() public view returns (uint256 total);
    function balanceOf(address _owner) public view returns (uint256 balance);
    function ownerOf(uint256 _tokenId) external view returns (address owner);
    function approve(address _to, uint256 _tokenId) external;
    function transfer(address _to, uint256 _tokenId) external;
    function transferFrom(address _from, address _to, uint256 _tokenId) external;
    event Transfer(address from, address to, uint256 tokenId);
    event Approval(address owner, address approved, uint256 tokenId);
    function supportsInterface(bytes4 _interfaceID) external view returns (bool);
}
contract MultiCat {
    ERC721 public target;
    struct Proposal {
        uint votesNeeded;
        uint action;
        address from;
        address to;
        uint tokenId;
        mapping (address => bool) voters;
    }
    mapping (address => bool) public owners;
    uint ownerCount;
    mapping (uint => Proposal) public proposals;
    uint proposalCount;
    function MultiCat () public {
        owners[msg.sender] = true;
        ownerCount = 1;
    }
    modifier onlyOwner() {
        if (!owners[msg.sender]) {
            revert();
        }
        _;
    }
    function vote (uint propsalId) onlyOwner public {
        Proposal storage proposal = proposals[propsalId];
        require(!proposal.voters[msg.sender]);
        proposal.votesNeeded--;
        proposal.voters[msg.sender] = true;
        if(proposal.votesNeeded == 0) {
            if(proposal.action == 0) { // transfer
                target.transfer(proposal.to, proposal.tokenId);
            }
            if(proposal.action == 1) { // transferFrom
                target.transferFrom(proposal.from, proposal.to, proposal.tokenId);
            }
            if(proposal.action == 2) { // addOwner
                owners[proposal.to] = true;
                ownerCount++;
            }
            if(proposal.action == 3) { // delOwner
                owners[proposal.to] = false;
                ownerCount--;
            }
        }
    }
    function transfer(address _to, uint _tokenId) onlyOwner public {
        proposals[proposalCount++] = Proposal(ownerCount, 0, 0x0, _to, _tokenId);
        vote(proposalCount-1);
    }
    function transferFrom(address _from, address _to, uint _tokenId) onlyOwner public {
        proposals[proposalCount++] = Proposal(ownerCount, 1, _from, _to, _tokenId);
        vote(proposalCount-1);
    }
    function addOwner(address _to) onlyOwner public {
        proposals[proposalCount++] = Proposal(ownerCount, 2, 0x0, _to, 0);
        vote(proposalCount-1);
    }
    function delOwner(address _to) onlyOwner public {
        proposals[proposalCount++] = Proposal(ownerCount, 3, 0x0, _to, 0);
        vote(proposalCount-1);
    }
}