Mile post properties (de: Hektometertafeleigenschaften)

The implementation of mile post panels may be back-traced following ticket #173 (closed).

During the railML conference in Berlin (2013-03-06) two aspects were shortly discussed:

• Are there any "switchable" mile posts in any country?

It seems a bit strange to change the shown mileage depending on whatever.

Current idea is, to remove the "switchable" attribute from the milepost element.

• Is a reference to mileageChanges needed?

Are there any mile post panels, that show both mileages (incoming and outgoing)?

If that is true, a "mileageChangeRef" and a "nextShowValue" attribute have to be added.