* [PM-1879] Replaced JsonSerializer.Serialize with CoreHelpers.ClassToJsonData
* [PM-1879] Changed OrganizationService.SaveUserAsync to check Custom permissions
* [PM-1879] Added unit tests for saving Custom permissions using a Custom user
* [PM-1879] Added method OrganizationUser.GetPermissions to deserialize the Permissions property
* [PM-1879] Refactored ValidateCustomPermissionsGrant to return bool
* [PM-1879] Added unit test SaveUser_WithCustomPermission_WhenUpgradingToAdmin_Throws