Github api auth. Github Pull request engine improvements to get pull and build status

Github Authentication will allow rate-limit of 5000 requests per hour vs 60 for none authenticated requests
```ruby
Onebox.options ={:GithubPullRequestOnebox => {
								:github_auth_token => "<token>",
								:github_auth_user  => "<user>",
								:github_auth_pass  => "<pass>",
								:github_auth_method =>:oauth, # :basic | :oauth | nil
								
								:get_build_status  => true
								}
}
```

Get Pull status , and build status
![image](https://cloud.githubusercontent.com/assets/8693091/4384106/976c0432-43b0-11e4-8ac0-2fded60c13bc.png)