Edit Documentation Button/Link

This adds a new usercontrol that tries to figure out the original path & casing of the markdown file, as GitHub is case sensitive for URLs to files in the source repository.

I could do with some help with a common CSS button to help style it.
Also if the url is modified in the address bar say someone changes casing of the URL in the address bar it will also not work

http://our.umbraco.org/documentation/Installation/Install-umbraco-manually

https://github.com/umbraco/Umbraco4Docs/blob/master/Documentation/Installation/install-umbraco-manually.md

and change it to 
http://our.umbraco.org/documentation/installation/Install-Umbraco-Manually 

https://github.com/umbraco/Umbraco4Docs/blob/master/Documentation/installation/Install-Umbraco-Manually.md

It will not work as this implementation uses the HttpContext Item of umbOriginalUrl to help build up the GitHub documentation URL, so if anyone has any suggestions on how to avoid this as well I would love to know.

Thanks,
Warren :)