Automatically install missing track libraries

See forum discussion from this post onwards - http://www.elvastower.com/forums/index.php?/topic/37130-request-for-new-openrailsorg-download-routes/page__view__findpost__p__297249

Open Rails would detect the need for XTracks or ScaleRail and offer to install it for the user.
It could do this when the route is being loaded, but even better if a reference to the track could be sought and found when the user presses Start or even when the route is added to the list of content.

If the process of installing hides or changes existing files, then this should be made clear to the user beforehand.