Added support for a new problem type: ChoicetextResponse
Updated behavior for split_answer_dict, get_score, and check_student_inputs (responsetypes.py)
Provide `set_many` methods for Lms and Mongo KeyValueStores

Refactor new set_many and update XBlock version number.
Provide implicit saves for XBlocks and XModules.

Update existing tests and provide new ones to test new paradigm.
Merge pull request #416 from edx/sarina/xblock-bulk-save-interface

Add XBlock bulk saves to LMS/CMS
Merge pull request #310 from robertjmarks/master

Adds in changes for stat2.3x question type
Generate TypeError if from or to_json fail.
Have save_item parse json formatted field values by type

including allowing javascript to serialize date/time natively.
json field value conversion test
Merge pull request #421 from edx/dhm/template_acceptance

Fix due/start date setting in edit_subsection
Use CodeJail with FSIZE support, and default to 50k
Merge pull request #435 from edx/ned/allow-tempfiles-in-sandbox

Use CodeJail with FSIZE support, and default to 50k
Merge branch 'master' of github.com:edx/edx-platform into feature/kluo/bulk-email
Add self to AUTHORS, feature to CHANGELOG