Closes#1134
Adds a `concurrency_index` column to `osm_route_member` as described in #1134. For example, listing concurrencies on a [segment of the Washington Bridge](https://www.openstreetmap.org/way/43080535) in Providence, Rhode Island, USA:
```
openmaptiles=# select osm_id, network, ref, network_type, name, concurrency_index from osm_route_member where member=43080535 order by concurrency_index asc;
osm_id | network | ref | network_type | name | concurrency_index
----------+---------+-----+---------------+---------------+-------------------
-1694950 | US:I | 195 | us-interstate | I 195 (RI/MA) | 1
-2308410 | US:US | 6 | us-highway | US 6 (RI) | 2
-1347856 | US:US | 1A | us-highway | US 1A (RI) | 3
-2309143 | US:US | 44 | us-highway | US 44 (RI) | 4
(4 rows)
```
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