Update schema documentation for railML 2.4

Description

The railML schema documentation needs to be generated according to the new XSDs.

Open Tasks

• XMLSpy schema documentation generated
• Update namespace information from 2016 to 2018

### Changesets
 * [changeset:"77X/railML"] - Documentation needs update 
 * [changeset:"77X/railML"] - XMLSpy schema documentation generated
 * [changeset:"77X/railML"] - Updated namespace information from 2016 to 2018