Take TTC vehicle mode from the fleet number before the route

Replacement buses on 5xx streetcar routes were drawn as streetcars, and
Flexity streetcars reporting no route were drawn as buses. A feed can now
supply vehicleMode(id); TTC maps 4400-4699 to streetcars and every other
fleet number to buses, falling back to the route otherwise.

CHANGELOG.md

@@ -4,7 +4,9 @@
   YRT/Viva, Guelph, Burlington, Barrie and Kingston, each carrying its own
   licence quote and attribution. A feed can now name its own modes, so Toronto's
   trams read "Streetcar" while Helsinki's stay "Tram", and a feed whose route ids
-  are internal keys can translate them to the number a rider would say.
+  are internal keys can translate them to the number a rider would say. TTC
+  vehicles take their mode from the fleet number first, so replacement buses on
+  streetcar routes read as buses and out-of-service streetcars stay streetcars.
 
 - Cyclone advisories no longer go dark while NHC publishes an advisory ahead
   of its nominal time: advisory and position times up to 90 minutes ahead of