Add chefspec to generators

Any recipe generated by `chef generate` should now also automatically have a corresponding spec file template generated in spec/unit/recipes. In addition, a spec/spec_helper.rb file will be created if one does not currently exist.

I also consolidated the redundant template/recipe.rb and template/default_recipe.rb files for easier maintenance.
This should be available via methods in `TemplateHelper`. We're explicitly avoiding passing in variables to the templates.