#1076 added a new class ModelInspector that could be used to eventually replace ModelDefinition. This requires some refactoring.

On top of that, ModelInspector could also add new methods like hasPrimaryKey, getPrimaryKeyName, getInverseKeyName, getInverseKeyProperty, etc. This then could replace all the places where we hard coded keys.

Finally, if ModelDefinition gets totally replaced, ModelInspector can be renamed to ModelDefinition, as it's a more logical name. We aren't able to do that just yet, because of the naming collision