Prevent T-junctions — Steam Revolution: The Age of Rail Steam update #47421

Made it an error for track vertices to be on other tracks. This was a bug to have been allowed in the first place. Unfortunately, there were some submitted solutions that became invalid due to this change.Fixed bug where routes from a signal were added multiple times and required removing all the dumplicates via UI to remove a path.Fixed bug where terminal signals weren't being correctly removed from route highlighting mode.Fixed buggy rendering where culling lagged behind for fast camera movement when following a train.