improve class=path styling (#1450)

This PR addresses that by:

* rendering oneway arrows on more than `subclass=cycleway`
* less opacity for path/footway casing
* adding the thin black casing to bridges
* adding `subclass=steps` & `subclass=bridleway` rendering
* render `bicycle=designated` as `subclass=cycleway` and `horse=designated` as `subclass=bridleway` (bike taking priority)
* improved tunnel rendering with double casing & adding main line
* made casing min zoom consistent across subclasses

All of these changes were made to mimic OSM Carto.

layers/aeroway/style.json

@@ -157,7 +157,7 @@
           "taxiway"
         ]
       ],
-      "order": 182
+      "order": 191
     },
     {
       "id": "airport_gate",
@@ -197,7 +197,7 @@
           "gate"
         ]
       ],
-      "order": 183
+      "order": 192
     }
   ]
 }