Add .ruby-version and .ruby-gemset to the application root

Since this is a Rails application we should have a .ruby-version and optionally a .ruby-gemset in the root to deal with multiple ruby managers. With these two files in place it'll help with compatibilty with all of the main ruby managers - rbenv, RVM, chruby, etc.

I grabbed the latest patch version of 2.0.0 as of today.