A bunch of clean-cut white guys — dressed all in white, to drive the point home — sing “We are Africa!” The dramaturgically unsound founding myth of the Mormon religion finds fitting analogues in “Star Wars” and “Lord of the Rings.” Seven years after its premiere, the Tony Award-winning “The Book of Mormon” is still priceless. Trey Parker, Robert Lopez and Matt Stone’s silly, raunchy musical comedy incisively encapsulates foibles — not just those of the Mormon religion, but those of the country where it was born.