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/transportation_name/style.json

@@ -34,7 +34,7 @@
           "ferry"
         ]
       ],
-      "order": 175
+      "order": 184
     },
     {
       "id": "road_label",
@@ -81,7 +81,7 @@
           "ferry"
         ]
       ],
-      "order": 176
+      "order": 185
     },
     {
       "id": "highway-shield-tertiary",
@@ -160,7 +160,7 @@
           "ref"
         ]
       ],
-      "order": 177
+      "order": 186
     },
     {
       "id": "highway-shield-secondary",
@@ -239,7 +239,7 @@
           "ref"
         ]
       ],
-      "order": 178
+      "order": 187
     },
     {
       "id": "highway-shield-primary",
@@ -318,7 +318,7 @@
           "ref"
         ]
       ],
-      "order": 179
+      "order": 188
     },
     {
       "id": "highway-shield-motorway",
@@ -400,7 +400,7 @@
           "ref"
         ]
       ],
-      "order": 180
+      "order": 189
     }
   ]
 }