Allow multiple validators

Switch User/Password/Role validators to IList instead of a single instance, this will allow us to split apart functionality i.e. (UniqueEmail, UniquePhoneNumber) instead of requiring one mega validator which should help with some of the validation extensibility issues

cc @divega @suhasj  
Sure. I thought it would be at par with the earlier experience that if no validator is passed we throw an error. If are choosing to be non blocking that is fine too