Update <xs:documentation> in <xs:annotation> (de: <xs:documentation> in <xs:annotation> aktualisieren)

The annotations in the current XSD's aren't updated since version 2.0 and will not express the current license situation:

<xs:annotation>
    <xs:documentation>Copyright (c) railML.org; All Rights Reserved.</xs:documentation>
    <xs:documentation>This work is licensed under a Creative Commons Attribution 2.0 License. http://www.railml.org/index.php/license.html</xs:documentation>
    <xs:documentation>For further information see: http://www.railml.org/</xs:documentation>
    <xs:documentation>Content of this file: XML Schema for railML(R) 2.2 Definition of root element "railml", refers to elements of all sub schemas from "xs:include" paths</xs:documentation>
</xs:annotation>

As written in the current license terms we're using a customized CC BY-NC-ND 3.0. This should be changed, together with a link the the new railML.org's website. A change from CC BY-NC-ND 3.0 to CC BY-NC-ND 4.0 should be taken into consideration.