add unit tests for Ping model and setup rails env for TravisCI
update Gemfile to Rails 4.
removed newrelic_api gem since it had a hard dependency on rails 3.0.7
https://github.com/newrelic/newrelic_api/blob/619595fe0e0b350248c9e26136afb516cc5f24ef/newrelic_api.gemspec
setup the envs with the default rails 4 configs
require sass after getting this warning on startup,

Started GET "/" for 127.0.0.1 at 2013-10-23 09:10:24 -0600
  ActiveRecord::SchemaMigration Load (0.4ms)  SELECT "schema_migrations".* FROM "schema_migrations"
Processing by StatusController#show as HTML
  Ping Load (0.5ms)  SELECT "pings".* FROM "pings"
  Rendered status/_pings.erb (0.7ms)
  Rendered status/show.html.erb within layouts/application (3.2ms)

WARN: tilt autoloading 'sass' in a non thread-safe way; explicit require 'sass' suggested.

  Rendered status/_current.html.erb (0.4ms)
Completed 200 OK in 249ms (Views: 229.5ms | ActiveRecord: 1.8ms)
load schema since "schema.rb" is in the git repo
Merge branch 'rails4'