* annotate --routes modifies only routes.rb

This change is a proposed solution to #357 and an alternative to the already proposed solution #361.
In #361 it is needed to call `annotate --routes --ignore-models` to achieve the same as in this change with only `annotate --routes`.

* Call eager_load only when models are included

This to prevent activerecord model errors when using mongoid for example and calling `annotate --routes`