Five Florida teenagers have been charged in the vicious, caught-on-video mob beating of a student at Marjory Stoneman Douglas High School — the site of one of the nation’s worst school shootings. The fifth teen linked to the savage Dec. 12 beating turned himself in at the Coral Springs Police Department on Monday morning — with cops still looking for one more suspect, WPLG-TV News reported. The disturbing video first posted by TMZ shows a lone teenager, who has not been identified, being attacked by a half-dozen students who kicked and punched him repeatedly — until one young brute hurls...