What’s clear: Navy football will join the Big East come 2015. What’s unclear: Everything else. From the size of the conference (13 teams in 2015, as planned, or an even number to avoid a scheduling nightmare?) to the fate of future TV deals to the structure of college football’s postseason, nothing is certain. But there’s at least a hint at one of the big mysteries — how the league will set up its two divisions. The Philadelphia Inquirer reports today that in 2013, with 12 teams likely participating, the conference will divide into East and West divisions, with geography the…