Prior to this change, `Annotate.include_models?` returned the inverse of `Annotate.include_routes?`. This made it so annotating models and routes was not possible to do together.

This PR adds an explicit `--models` flag and also adds it the option to `lib/generators/annotate/templates/auto_annotate_models.rake` with the default being set to `false`. 

Fixes #563 and undoes the bug introduced in #485.