[RJA-1531][fix] Roles: null is displayed instead of last name when is it doesn't exist
[RJA-1589][fix] REST: Roles: Nonexistent user and group were added to project roles (ldap was configured)
  - disabled user/groups validation in system settings;
  - added responses about nonexistent users to REST methods;
  - updated services;
  - made refactoring;
Merge pull request #779 from azhuchkov/disable-validation

Disable roles validation