re #33: load frontend app configuration from config.json file
re #37 protect getUser and getUsers processes on server-side
Related refactoring - moving relevant logic to UserManager interfaceand to /users API endpoint.
re #37 make UI compatible with new User controller API
Error and information messages modified - correct error messages from backend are displayed and information messages are translated
Modified api users service, fixed edit settings dialog
Re#7527 SnackBar opens if the error occurs
Refactor service structure