Add suburb, quarter, neighborhood rendering

[wmisener]

This PR renders urban districts (OSM place=suburb, place=quarter, and place=neighbourhood), resolving #1058. Urban districts are rendered in all caps with a dark blue font color, the same font color as currently used for waterway label. However, waterway labels are always mixed case and italicized, so I think the risk of confusion is low. The color and capitalization, along with the lack of a dot, distinguishes urban districts from the 'independent' place hierarchy (i.e. city, town, village).

Since the distinction in OSM between each place value in American usage is fuzzy at best, all three classes are rendered similarly. The only differences are zoom level and font size. Suburbs appear between z11-z15, quarters between z14-z16, and neighbourhoods between z14-z17. I would've liked quarters to appear at z13, but they only begin to appear in the tiles at z14. The maximum zooms ensure that the labels disappear to make room for POIs once you are at high zoom.

In the legend, I labeled suburb "Major district", quarter "Large neighborhood", and neighbourhood "Neighborhood". Though maybe all three could just be grouped together?

Samples: Los Angeles, z11 (localhost)

San Francisco-Oakland, z11 (localhost)

Oakland, z12 (localhost)

Midtown Manhattan, z14 (localhost)

Manhattan, z16 (localhost)

Marina del Rey, z14 (localhost) Compare the place=quarter (top) to the natural=water (bottom)

Legend, z14 (localhost)