Evaluating the Effectiveness of a Mobile HIV Prevention App to Increase HIV and Sexually Transmitted Infection Testing and Pre-Exposure Prophylaxis Initiation Among Rural Men Who Have Sex With Men in the Southern United States: Protocol for a Randomized Controlled Trial - Jeb Jones; Georgia Manley; Tiffany R Glynn; Kristin M Wall; Stefan D Baral; E Danny Harris; David Benkeser; Patrick S Sullivan (JMIR Research Protocols)