monitor_id now can be null
add online class adding function
rename folder
done adding category function
Merge branch 'master' of github.com:heroandtn3/bksmooc

Conflicts:
	src/bksmooc/model/dao/mysql/CategoryDbMySql.java
	src/bksmooc/model/dao/mysql/CourseDbMySql.java
	src/bksmooc/model/dao/mysql/OnlineClassDbMySql.java