A Special Olympian took center stage at Wrigley Field Monday night. Stefan Xidas sang the national anthem ahead of the Cubs game against the Brewers.   Stefan Xidas sang the national anthem on #AuthenticFan night, after raising $18,000 for Special Olympics…which will be matched by @Cubs charities. pic.twitter.com/5eazMJxM6f — NBC Sports Chicago (@NBCSChicago) September 11,…