fix check_in
fix json
Merge branch 'Bohan-Zheng' into rtong

Conflicts:
	app/controllers/StudyPlanController2.java
comment display function for xiaoran to test
Merge branch 'rtong'
submit button on  student/index

submit button
Merge branch 'master' into rtong
add semester page
Merge remote-tracking branch 'origin/Bohan-Zheng' into bowen
null to []
add null manipulation
merge with bohan and update database
Merge branch 'bowen' into rtong
Merge remote-tracking branch 'origin/rtong' into bowen
Finish CheckInSelectedCourse and CheckAllSimpleAnd Complex interfaces
Merge branch 'rtong' into shuaiwang

Conflicts:
	app/controllers/StudyPlanController.java
	app/controllers/algorithm/req_and_course/TestLinkList.java
add step1 function
Merge branch 'Bohan-Zheng' into rtong
Merge branch 'shuaiwang' into rtong
Merge branch 'Bohan-Zheng' into rtong