Feature:Onebox Github Gist, Support Multiple files gist, Line or Range Selection, Show line numbers

Gist Onebox - now with line numbers and line selectors. same logic from the githubblob engine.
and support multi file gists.


Gist without a permalink hash will return the first file found returned by the gist api
Permalink hash might match multiple files in the repository (rarely)  => Will return the first file found returned by the gist api

### Line Range
![image](https://cloud.githubusercontent.com/assets/8693091/4608917/2b713058-528e-11e4-9fc8-9e688d3e09a5.png)

### Single Line 

![image](https://cloud.githubusercontent.com/assets/8693091/4608922/4fbf32d4-528e-11e4-9334-53794a1abdc1.png)

### Different Revision
![image](https://cloud.githubusercontent.com/assets/8693091/4608935/8a57eaee-528e-11e4-8820-4fae9cfe61ea.png)