Allow specification of different violation levels/scope for the same rule

[elmoeleven]

We should be able to support a config like this:

{
  "Name": "NoMissingObjectReferences",
  "ViolationLevel": "Error",
  "ViolationScope": "Scene",
  "Exclusions": []
},
{
  "Name": "NoMissingObjectReferences",
  "ViolationLevel": "Warning",
  "ViolationScope": "Prefab",
  "Exclusions": []
}