Converse, Inverse, and Contrapositive fixes

Fix up a bunch of the questions in Converse, Inverse, and Contrapositive so that they make more sense.

Exercise: http://sandcastle.khanacademy.org/media/castles/xymostech:converse_inverse_contra/exercises/converse_inverse_and_contrapositive.html?debug

Examples of differences:

Old: http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/converse_inverse_and_contrapositive.html?debug&problem=elephants-and-peanuts&seed=127859989
New: http://sandcastle.khanacademy.org/media/castles/xymostech:converse_inverse_contra/exercises/converse_inverse_and_contrapositive.html?debug&problem=elephants-and-peanuts&seed=127859989

Old: http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/converse_inverse_and_contrapositive.html?debug&problem=vertical-and-congruent-angles&seed=242638339
New: http://sandcastle.khanacademy.org/media/castles/xymostech:converse_inverse_contra/exercises/converse_inverse_and_contrapositive.html?debug&problem=vertical-and-congruent-angles&seed=242638339

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