Contract Source Code:

pragma solidity ^0.5.0;

contract Proxy {
    address public owner;
    address public target;

    event ProxyTargetSet(address target);
    event ProxyOwnerChanged(address owner);

    constructor() public {
        owner = msg.sender;
    }

    /**
   * @dev Throws if called by any account other than the owner.
   */
    modifier onlyOwner() {
        require(msg.sender == owner);
        _;
    }

    function setTarget(address _target) public onlyOwner {
        target = _target;
        emit ProxyTargetSet(_target);
    }

    function setOwner(address _owner) public onlyOwner {
        owner = _owner;
        emit ProxyOwnerChanged(_owner);
    }

    function() external payable {
        address _impl = target;
        require(_impl != address(0));

        assembly {
            let ptr := mload(0x40)
            calldatacopy(ptr, 0, calldatasize)
            let result := delegatecall(gas, _impl, ptr, calldatasize, 0, 0)
            let size := returndatasize
            returndatacopy(ptr, 0, size)

            switch result
                case 0 {
                    revert(ptr, size)
                }
                default {
                    return(ptr, size)
                }
        }
    }
}