Pull request adding a mega-test for the entire Rails Example Apps system, along with mega Rake commands

This pull request should ease development of r_a_c, especially by developers relatively new to it. It supplies a "full ecosystem" automated test for developers.

The only way to know for sure that changes to r_a_c do not break any Rails Example Application is by regenerating each example application and running its test suite.

To greatly ease the process, this pull request provides an automated Rake task (see [instructions](https://github.com/MarkDBlackwell/rails_apps_composer/blob/feature_megatest/megatest/README.txt)) to do just that, by regenerating and testing all the Rails Example Applications.

It also includes several useful new Rake tasks which operate (in batch) over the collection of Rails Example Apps (see `rake --tasks`).

It works only for people running the Bash shell (and likely also the Bourne shell).

This pull request should not affect the ordinary users of the gem, nor its ordinary functionality, but only is useful to its gem developers.

The new mega-test passes. It regenerates eight (8) Rails Example Apps and runs their tests.

Actually, the mega-test will pass if certain pull requests (to the Rails Example Apps) are accepted (which I have submitted to help them generate without error). :)

All rails_apps_composer tests (`rake default`) also pass.