Small signal update

This update adds an alternative set of lower-quadrant semaphore signals in the Great Western Railway style. These signals have been fitted to the Westfords route.

If you've made a route yourself the easiest way to change the signals is by opening the Route properties in the editor and clicking the Swap signal types button. Signals can also be changed individually by left clicking them and changing the type in the side panel.

This update also fixes fences across tracks and too low road bridges in some routes.