Restore rendering of service roads and living_streets in tunnels and on bridges
Resolve bug that causes spur, siding and yard not to render properly
 Do not hide some bridges in z12/z13

- Do not hide secondary road bridges on z12
- Do not hide tertiary, residential, unclassified, and road bridges on z13

Conflicts:

	roads.mss
Collapse definitions for normal roads, tunnels and bridges

This collapses, per road type, definitions that are the same for normal
roads, tunnels and/or bridges.
In addition, it gives some instances clearer names.
This makes it more easy to maintain the code, and to detect inconsistent
definitions.

Changes in rendering:
* Render minor service roads on bridges and tunnels smaller and on higher
  zoomlevels only, just like minor service roads that are not on a
  bridge or tunnel. This solves #269 on Github and 3883 on trac.
* Restore bridges of bridleway, footway, cycleway, path, lightrail on
  z13.