Only setup SendGrid in production env.

This is as recommended in the instructions for migrating from Bamboo to
Cedar Heroku stack.
Specify Ruby 1.9.3 for use on Heroku Cedar stack.
Update schema based on running migrations on empty database.
Remove heroku gem from bundle. I'm now using heroku toolbelt.

There was a conflict with the Gemfile.lock so I reverted to my version and ran
`bundle install` to fix it up.
Update to Rails 3.2.13
Update bundled gems

I ran `bundle update`. This update includes the latest Mocha, which removes
the deprecation warnings (warning: already initialized constant Mocha).