Get rid of excessive whitespace due to graphies in hints.

How? By moving the graphie init into the hints as well, and using code
blocks instead of graphie labels for the questions.

Test Plan:
Run khan-exercises on port 8765, then go to the following urls and make
sure that whitespace looks normal.

http://localhost:8765/exercises/adding_negative_numbers.html?debug&problem=PLUS

http://localhost:8765/exercises/adding_and_subtracting_negative_numbers.html?debug&problem=PLUS
http://localhost:8765/exercises/adding_and_subtracting_negative_numbers.html?debug&problem=MINUS

http://localhost:8765/exercises/division_0.5.html?debug&problem=0

http://localhost:8765/exercises/multiplication_0.5.html?debug&problem=missing-C
http://localhost:8765/exercises/multiplication_0.5.html?debug&problem=missing-B

Auditors: eater, cameron