1. Remove checkpoints field from get  challenge detail api

2. Allow return checkpoints submissions in get submissions API.

3. Add SUBMISSION_TYPE in initizlizers/helper.js
Update change log in actions/challenges.js
Merge remote-tracking branch 'upstream/master' into submissions_api_update

Conflicts:
	actions/challenges.js
	initializers/helper.js
Fix jslint error
Merge pull request #232 from Ghost141/submissions_api_update

Submissions api update