Support Desktop in Clone

Support for `Desktop in Clone` by `github-windows://` and `github-mac://` protocol

(ssh & http)

![clone in desktop](https://cloud.githubusercontent.com/assets/1309468/3890451/abb9de36-221e-11e4-9ca6-795391e645eb.png)

`userAgent` is not exact property name. I think it should be another name such as `platform`.