Validate resolver before starting

[chuwy]

When we had apikey instead of apiKey - it just ignored the key and used unautheticated request, while the config was clearly invalid against its schema.

[istreeter]

I implemented this, but I am unhappy with the implementation, because it involved adding 5 versions of the resolver-config schemas to the app's resources/iglu-client-embedded directory. I think this validation is better done in iglu-scala-client, so I opened this issue over there.