#13 Add get Role tag method.

It's will use in Database.
#13 Add configuration ORM class.

Just have key and value.
#13 Add DAO method and some method.
#13 edited database structure.

- Removed "id" field, used "key" field for primary key.
#13 Defined some configuration to save.
Merge pull request #18 from MilesChou/13-config-class

Config class finished
#19 Renamed activity.
#19 Renamed layout XML.
#19 Server build activity finished.
#19 Teacher check SN activity finished.
#19 Teacher login activity finished.
#19 closed. Bug fixed.
Merge pull request #20 from MilesChou/19-teacher-module-rebuild

Teacher module rebuild