Rearrange code between Viewer3D and RenderProcess.
Rewrite Trains, Terrain and Scenery thread-safe code.
Split out 'world' from 'viewer' code and data.
Remove and collapse some unnecessary extra methods in favour of doing more in constructors.
git-svn-id: http://svn.uktrainsim.com/svn/openrails/trunk@976 a9f3cfff-6c41-7446-b0ca-052bd761e6eb