Add: Conditional Statements 1

Taken from pull request:
https://github.com/Khan/khan-exercises/pull/18972

Moved things from word_problems into the exercise. Reformatted to use
the new style

http://sandcastle.khanacademy.org/media/castles/xymostech:conditional_1/exercises/conditional_statements_1.html

@spicyj @beneater