On a busy Friday night, the challenge at Mary Margaret’s Olde Irish Tavern is not finding a good pint of Guinness. It is finding a place to sit, order dinner, or even make it to the restroom. The downtown St. Pete pub is often filled shoulder to shoulder with live-music fans, soccer supporters, dinner guests, and late-night crowds. Owner Pete Boland, who also owns The Galley and The Ship’s Hold, said the space has become so consistently busy tha…