Add labels for rendered landuse and leisure polygons

Add labels for rendered landuse and leisure polygons

This shows name labels for all rendered leisure/landuse polygons. That is:
* leisure: swimming_pool, stadium, sports_centre, playground, park, recreation_ground, common, garden, golf_course
* landuse: quarry, vineyard, orchard, cemetery, grave_yard, residential, garages, field, meadow, grass, allotments, forest, farmyard, farm, farmland, recreation_ground, conservation, village_green, retail, industrial, railway, commercial, brownfield, landfill, greenfield, construction, military

Notes:
* Unifies polygon/point labels in amenity-points.
* park-text merged into amenity-points text. The "text"/"text-poly" layers were doing roughly the same thing except unified between points and polygons. (Note leisure=marina, for instance.)
* Removes the now superfluous point=yes catchall.
* Text color is mostly the `darken()`ed color of the polygon.
* Halo 2px->1px (the more common value) for most of these labels now. Exceptions are cemetery and vineyard, which needed stronger halos to override the background pattern.
* swimming_pool name will now render at z17+. Everything else renders at z15+, like it did before. We can tweak all this now that they're split up.
* Darkens the danger_area text color (was pink on pink).

The following image shows the various types of polygon/text renderings at z18. (This is not all the features with names.)

![boxes osm 18](https://f.cloud.github.com/assets/1147239/2239409/d933b6fa-9c2e-11e3-82bc-20409f0b4c98.png)