Amanda Lipitz’s documentary “Step” is one of the biggest crowd-pleasers at the 2017 Sundance Film Festival, and deservedly so, as it exuberantly tells the life-affirming story of a remarkable group of young women in inner-city Baltimore. The Baltimore Leadership School for Young Women was founded in 2009 with a handful of sixth-graders who, as the movie starts in fall 2015, are in their senior year.