Issue 336 rake tasks

[eoinkelly]

Closes #336

• Add the records counting rake task within the app namespace. Include a comment guiding devs on what should go in app namespace.
• Create an empty dev namespace with a comment guiding devs on what to put there
• Document the tasks in the app and dev namespaces in the README
• rails new does not generate a README.rdoc anymore so we don't need to remove it

[eoinkelly]

The output in README.md looks like this after this change:

...snip...

Rake tasks

# App tasks (useful in local development and deployed environments)
rails app:db_stats                       # Print (to STDOUT) count of records in DB for each ActiveRecord model
rails app:template                       # Applies the template supplied by LOCATION=(/path/to/template) or URL
rails app:update                         # Update configs and some other initially generated files (or use just update:configs or update:bin)


# Dev tasks (useful in local development only)

...snip...