added assosiation database between user and group

...java/ntnu/idatt2016/v233/SmartMat/entity/group/Group.java

...u/idatt2016/v233/SmartMat/entity/group/UserGroupAsso.java

...tnu/idatt2016/v233/SmartMat/entity/group/UserGroupId.java

...n/java/ntnu/idatt2016/v233/SmartMat/entity/user/User.java

...33/SmartMat/repository/group/UserGroupAssoRepository.java

...att2016/v233/SmartMat/repository/user/UserRepository.java

...016/v233/SmartMat/service/group/UserGroupAssoService.java

...tnu/idatt2016/v233/SmartMat/service/user/UserService.java

src/main/resources/db/sql/dbschema.sql

...016/v233/SmartMat/controller/user/UserControllerTest.java

...datt2016/v233/SmartMat/repository/UserRepositoryTest.java

...6/v233/SmartMat/repository/group/GroupRepositoryTest.java

...martMat/repository/group/UserGroupAssoRepositoryTest.java

...v233/SmartMat/service/group/UserGroupAssoServiceTest.java

...idatt2016/v233/SmartMat/service/user/UserServiceTest.java