Add Nova Scotia shields

[claysmalley]

Adds shields for Nova Scotia. This introduces a new shield for 100-series "Arterial" routes, and factors the US route shield into a generic reusable shield, as this design has been reused in a few parts of the Western Hemisphere.

Nova Scotia's one- and two-digit routes are Trunk highways (network=CA:NS:T). Shields for these highways have a suspiciously similar design to US routes. I'm not quite sure of the history behind this, or who did what first, but they're almost identical, except for the white background where the US shield has a black background.

Nova Scotia's 100-series is Arterial highways (network=CA:NS:H), which are limited-access highways similar to Ontario's 400-series, Quebec's Autoroutes, or the Interstate system in the US. The design introduced in this PR removes all the red details on the yellow shield-within-a-shield, compresses the flag vertically and adjusts the colours to match the existing palette.

Nova Scotia's 200- and 300-series are Collector highways (network=CA:NS:R), linking rural areas to population centres. These have a simple brown rectangular shield with white text, almost identical to National Forest Roads in the US (#246).

[1ec5]

The arterial shield is beautiful – gives me hope that someday we can find a way to squeeze a little more detail into shields like South Carolina’s without sacrificing legibility.

[claysmalley]

Once we have a complete inventory of shields, we can spend some time refining the earliest ones. I have improvements in mind for the Carolinas 😄

[ZeLonewolf]

The arterial shield is beautiful – gives me hope that someday we can find a way to squeeze a little more detail into shields like South Carolina’s without sacrificing legibility.

Legibility of the text... you certainly can't tell that there's a red dragon in there ;)

[ZeLonewolf]

Looks good!