Upgrade to Ruby 2.1.1 and Rails 4.0.3

While this is running on the latest Ruby/Rails, it includes some gems
that provide backwards compatibility for Rails 3.x. Further work is
required to be completely migrated to 4.x. Some gems are still behind as
well, and will need more work than a simple upgrade (e.g. bootstrap).
Use dotenv gem for development and test
Add Heroku integration gem for production/staging
Load city image via asset pipeline
Use binding_of_caller gem in development

This provides REPL support in development when a 500 error occurs.
Move to strong_parameters
Merge branch 'rails4'