Megan FeldmanWhen you're riding a clear bike path near Rochester Park, just remember who to thank.On a 103-degree day like today, most people stick to air-conditioned buildings or poolside recliners. Not 19-year-old Jonathon Jackson.With a crew of a dozen other teens, the South Oak Cliff High graduate spent the afternoon trudging through the Great Trinity Forest in snake chaps and a work helmet to help restore a three-mile bike trail near Rochester Park. It's but one of several projects champio