Content Manager: make Consist and Car follow the new model design.
Additional MSTS format class, WAGFile, which is only used by the Content Manager (but belongs in Orts.Formats.Msts).
git-svn-id: http://svn.uktrainsim.com/svn/openrails/trunk@3134 a9f3cfff-6c41-7446-b0ca-052bd761e6eb