dz4
fix. add AccountService
change .gitignore
fix. if user does not exist, return error
Add MessageService and other
refactoring
refactoring complete
delete magic const
Refactoring: optimized imports, resolved some problems after code inspection(problems, that are not resolved now, will be automatically resolved after merge).
Refactoring: moved variables to the top in Frontend.
Merge branch 'dz4':
+Added MessageSystem
+Added AccountService