Added text match assessment type.
Refactored some of the Match/Multi code to accommodate new puzzle type.

filter "onComplete" function from milestone POST requests
add configurable textarea placeholder text to text_match puzzle type
fix comment in seed.rake
Update .gitignore
re-apply changes to data.en.yml
Update _text_match.html.haml

fix dom class name
Update data.en.yml
Delete test_open_response_assessment.ora.txt
Merge pull request #256 from code-dot-org/msm_assessments

(Msm assessments) Text Match puzzle type for mathematical expressions