Students in Greater Bangor on Friday morning formed the latest wave of young people to walk out of classes to protest gun violence. They joined thousands of other teens and teachers who, over the course of the week, congregated at 10 a.m. on the pavement outside of their schools for 17 minutes — one for each of the students gunned down in the hallways of a Parkland, Florida high school a month earlier. Theirs was the third day of demonstrations, after a nor’easter this week forced schools to close and students to stagger their walkouts over the remainder of the week. In Brewer, more than 100 students walked out of class and into the gym, joined by members of Brewer’s police force and city council.