Add network to transport layer (#1158)

Closes #1153 

This PR populates the existing `network_type` field in the route table with highway route network information, using the most important value in cases of concurrencies.  In order to expose this value, two files `network_type.sql` and `update_route_member.sql` were moved from the `transportation_name` layer to the `transportation` layer.

Below is a representative zoom level 6 with motorways only shown for `us-interstate` network types.  This sample was generated from this PR using a [custom branch](https://github.com/ZeLonewolf/openstreetmap-americana/tree/selective-highway-zoom) of openstreetmap-americana.  This provides a simplified rendering of the highway network which excludes many minor motorway roads and sections.
![image](https://user-images.githubusercontent.com/3254090/126420985-c380b54b-a991-4a7c-a4c1-40a5cf5ec6b0.png)

Below is zoom level 6 on the current [openstreetmap-americana](https://zelonewolf.github.io/openstreetmap-americana/#6/42.148/-73.712).  Notice the many additional stubs, motorway islands, and minor routes which are present.  Instead of rendering `highway=trunk` to make this network look nice, we can instead suppress non-interstate roads and withhold motorway+trunk rendering to a closer zoom:
![image](https://user-images.githubusercontent.com/3254090/126421148-71e780ec-991d-4e38-a82a-85015b349e97.png)

layers/transportation/transportation.yaml

@@ -111,6 +111,12 @@ layer:
       - bridleway
       - corridor
       - platform
+    network:
+      description: |
+          The network type derived mainly from [`network`](http://wiki.openstreetmap.org/wiki/Key:network) tag of the road.
+          See more info about [`us-*`](http://wiki.openstreetmap.org/wiki/Road_signs_in_the_United_States),
+          [`ca-transcanada`](https://en.wikipedia.org/wiki/Trans-Canada_Highway),
+          or [`gb-*`](http://wiki.openstreetmap.org/wiki/United_Kingdom_Tagging_Guidelines#UK_roads).
     brunnel:
       description: |
           Mark whether way is a tunnel or bridge.
@@ -174,9 +180,11 @@ layer:
   datasource:
     geometry_field: geometry
     srid: 900913
-    query: (SELECT geometry, class, subclass, oneway, ramp, brunnel, service, layer, level, indoor, bicycle, foot, horse, mtb_scale, surface FROM layer_transportation(!bbox!, z(!scale_denominator!))) AS t
+    query: (SELECT geometry, class, subclass, network, oneway, ramp, brunnel, service, layer, level, indoor, bicycle, foot, horse, mtb_scale, surface FROM layer_transportation(!bbox!, z(!scale_denominator!))) AS t
 schema:
+  - ./network_type.sql
   - ./class.sql
+  - ./update_route_member.sql
   - ./update_transportation_merge.sql
   - ./transportation.sql
 datasources: