Update documentation to use URI notation instead of a source object

[original issue](https://github.com/IntrospectiveSystems/xGraph/issues/64)

> Found from setup in the "Build a Test System" documentation
> 
> Change
> 
> ```
> "Core": {
>     "Host": "modulebroker.xgraphdev.com"
> }
> ```
> to
> 
> ```
> "Core": "mb://modulebroker.xgraphdev.com"
> ```

