Handle urls that don't support x-callback spec

This pull request adds the possibility to manage urls that don't have the host set to `x-callback-url`.

For example, for this x-callback url:

    myapp://x-callback-url/action_name?para1=val1(...)

this url is also supported: 

    myapp://action_name?para1=val1

The goal is to support urls with a more simple syntax and so, easier to type by end-users in apps like [Launch-Center](http://appcubby.com/launch-center/).