update database
add student
move class to admin package
Change the way of detect whether user is login or not
Add submit error
show students list
Merge branch 'master' of github.com:heroandtn3/bksmooc

Conflicts:
	.settings/org.eclipse.core.resources.prefs
	src/bksmooc/model/dao/JdbcConnectorMySql.java
	src/bksmooc/model/dao/mysql/StudentDbMySql.java
	src/bksmooc/model/entity/OnlineClass.java
Remove some warning
Fix new way to check user is login or not