Add an configuration option for xmlSiteUrl

[Konafets]

The parameter xmlSiteUrl is currently configurable via the scheduler argument. In multi-stage environments (local, dev, stage, prod) this is not useful, as the data gets overridden by deployment.

It should be able to store the value of the argument in a environment specific configuration file and will be read from there at runtime. I think about a 2-step configuration:

1. If the user specifies the value inside the task, it will be taken from there
2. If the user does not specifies the value inside the task, the ext looks inside the configuration file
3. In case both are empty, an runtime exception will be thrown.