Basic destination sign handling.

This first part in our Exit Sign / Destination Sign quest re-wires
the `destination=` and `destination:ref=` tag to the `ref=` tag (in case
it's the highway does not already have a `ref=` tag).

Doing some analysis on both Berlin and San Francisco it looks like this
will add a couple of thousand `ref=` tags that we will announce in guidance.

References:
- https://github.com/Project-OSRM/osrm-backend/issues/2267#issuecomment-214771682
- http://wiki.openstreetmap.org/wiki/Key:destination
- http://wiki.openstreetmap.org/wiki/Proposed_features/Destination_details

features/guidance/destination-signs.feature

@@ -0,0 +1,33 @@
+@routing @guidance
+Feature: Destination Signs
+
+    Background:
+        Given the profile "car"
+
+    Scenario: Car - route name assembly with destination signs
+        Given the node map
+          | a | b |
+          | c | d |
+          | e | f |
+          | g | h |
+          | i | j |
+          | k | l |
+          | m | n |
+
+        And the ways
+          | nodes | name | ref | destination | destination:ref |
+          | ab    | AB   | E1  |             |                 |
+          | cd    | CD   |     | Berlin      |                 |
+          | ef    | EF   |     | Berlin      | A1              |
+          | gh    |      |     | Berlin      | A1              |
+          | ij    |      |     | Berlin      |                 |
+          | kl    | KL   | E1  | Berlin      | A1              |
+
+        When I route I should get
+          | from | to | route                           |
+          | a    | b  | AB (E1),AB (E1)                 |
+          | c    | d  | CD (Berlin),CD (Berlin)         |
+          | e    | f  | EF (A1: Berlin),EF (A1: Berlin) |
+          | g    | h  | ,                               |
+          | i    | j  | ,                               |
+          | k    | l  | KL (E1),KL (E1)                 |