update attributes in coding_question create
set default mem time attempt limit to coding questions
set auto_graded to true if coding question is in training
Merge pull request #228 from wangqiang1208/bugfixing/mission-attempt-left

Accept & set default value of coding questions
remove function set hints in trainings
Merge pull request #235 from wangqiang1208/bugfixing/mission-hints-for-private-test

remove function set hints in trainings
Merge branch 'development' of github.com:Coursemology/coursemology.org into Deploy