Pull request adding source signposts to generated templates

Currently when Rails Apps Composer generates a template it doesn't completely label it (internally) to show in detail the various source files from which it was generated.

Although its experts know where everything in each generated template comes from, more explicit signposts IMHO would help introduce it to hackers.

One important generated template is Rails Composer. The natural mystery of where all its source comes from is mentioned in its [issue #102](https://github.com/RailsApps/rails-composer/issues/102). Its template file [composer.rb](https://github.com/RailsApps/rails-composer/blob/master/composer.rb) (generated by gem Rails Apps Composer) directly runs Rails Composer (per its README section [Creating a Starter App](https://github.com/RailsApps/rails-composer/blob/master/README.textile#creating-a-starter-app)).

To help beginning Rails Composer hackers contribute, this pull request explicitly source labels each part of each generated template file. Actually its effect is broader than just on Rails Composer.

Also this pull request tidies up the number of blank lines here and there in an aesthetic way in generated templates while carefully preserving existing double spacing.

All tests pass, and core and railsapps recipes successfully are generated.