Partial harmonisation of simple types (de: Teilharmonisierung der Datentypen)

The issue of consistent simple types is currently filed in #317 for railML 3.1 and discussed in railML's misc forum.

Before a complete new modeling for the consistent use of the SI units, railML 2.4 already offers some 1:1 possible conversions of data types in order to simplify the use.

This concerns:

• tVMax to be migrated to tSpeedKmPerHour
• tEffortNewton to be migrated to tForceNewton
• ...