Refactor cache_question_or_answer_corresponding_to_requirement
Remove unnecessary private blocks
Refactor compute_levels
Refactor calculate_if_requirement_met_by_responses
Split response_level_index into more methods
D'oh
Rename *_corresponding_to_requirement
Refactor question and answer corresponding stuff
Grrrr
Merge pull request #849 from theodi/feature-improve-question-model-gpa

Refactor Question method