Added support for more verbose includes

New options:
  - Scope.includes([{model: App.Operator}])
  - Scope.includes([{association: "Operators"}])
Adds support for nested eager loading

Unfortunately it is limited by an issue with postgres:

https://github.com/sequelize/sequelize/issues/2084
Merge pull request #12 from komola/refactor/nestedEagerLoading

Nested eager loading