CourseDao refactoring + another part of tests for Group
 Changes to be committed:
	modified:   school-dao/src/main/java/school/dao/CourseDao.java
	modified:   school-dao/src/main/java/school/dao/implementation/CourseDaoImpl.java
	modified:   school-dao/src/test/java/school/dao/implementation/CourseDaoImplTest.java
	modified:   school-dao/src/test/java/school/dao/implementation/JournalDaoImplTest.java
	modified:   school-service/src/main/java/school/service/GroupService.java
	modified:   school-service/src/main/java/school/service/implementation/GroupServiceImpl.java
	modified:   school-service/src/test/java/school/service/implementation/GroupServiceImplTest.java
	modified:   school-web/src/main/java/school/controller/GroupController.java