1121313
algorithm pre_and_core
Merge branch 'shuaiwang' into rtong

Conflicts:
	app/controllers/StudyPlanController.java
	app/controllers/algorithm/pre_and_core/Course_Selection.java
	conf/application.conf
Merge branch 'rtong' into shuaiwang
fix bug: if a simple requirement already exists
fix addCourse
111
Merge branch 'shuaiwang' into rtong

Conflicts:
	app/controllers/StudyPlanController.java
fix hashmap bug
continue fix addCourse
Merge branch 'rtong' into shuaiwang

Conflicts:
	app/controllers/StudyPlanController.java
Merge branch 'shuaiwang' into rtong
Merge branch 'bowen' into rtong
fix json
Merge branch 'rtong' into Bohan-Zheng

Conflicts:
	.gitignore
	.target/views/course_list.scala.html
	build.sbt
	conf/application.conf