Collapse roads

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 tunnes 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.

This PR depends on 3c74350f473fe4581646eb39c0024fe167bd4f17, 541aa945fc27155c0973a01ae78750c3e6a625b8, and c60c07703852193caf28b3e6e917655d31eb1c99.