Commented Task: Implement UserQueryValidator.IsUserDTOValid() [1944]

We currently rely on UserDTO.HasValidId(). The issue with this is that we need to check for null each time we are generating a query.
This consequently multiply the number of tests by 2.
Update all the queries using HasValidId to use the UserQueryValidator.IsUserDTOValid() method.
Comments: Associated with changeset 33781: Version 0.9.0.0
- Tested MessageQueryGenerator
- Added Id condition on CanMessageBeDestroyed
- Added UserQueryValidator
- Added checks for ScreenName
- Added check for MessageId parameter
- Updated tests to cope with new code logic for checks
- Added a TestHelper to simplify the creation of random id and string