Add role to install ruby 2.1.2 from source, create Railsapp host

* Installing ruby from source and using a bin suffix (instead of using
  rvm or rbenv) reduces the number of moving parts and gives you more
  control over the application
* Also install rubygems and bundler while we're at it.
* Fun fact: installing rubygems from source causes the `gem` command
  to inherit the prefixes and suffixes of the ruby binary that called
  `ruby setup.rb`.