The on-again, off-again effort to open 60 tiny homes for the homeless is complete, though a large fence surrounds the entrance of the new facility called “Mission Cabins” in apparent hopes that passersby won’t notice it.Back in 2016, developers had hoped to turn the former Walgreens at 16th Street BART Plaza into a giant luxury condo project that critics nicknamed the “Monster in the Mission.” But that whole deal fell through before the pandemic…