Render access restrictions at the same time as the roads to which they apply

Access restrictions are now rendered at the same time as the roads they apply to.
This prevents access restrictions from overlapping with roads they don't apply to.
This is accomplished by putting roads-fill and the bridge layers in the access class, and removing all separate access layers.

This affects rendering as follows:
Access restrictions are only displayed on top of the road they apply to, not on top of neighbouring roads.
This change does not affect rendering in any other way.
Merge branch 'roadsv3.0' into roadsv4.0
Merge layers of bridges (for each osm-layer)

For each osm-layer, we merge the directions layer of bridges into the general layer of bridges.
This is done in preparation for removing the duplication of bridge layers for each osm-layer.

This does not affect rendering.
Merge layers for bridges using group-by

The 6 layers for bridges (one per osm-layer) are merged and replaced by a group-by construction.
This removes duplication in the code.

This change does not affect rendering.
Merge branch 'roadsv3.0' into roadsv4.0
Merge branch 'roadsv3.0' into roads-bridges
Merge branch 'roadsv3.0' into roads-bridges2
Add missing 'directions' classes
Merge branch 'roads-bridges' into roads-bridges2

Conflicts:
	project.mml
Merge #tracks-tunnels and #footbikecycle-tunnels into #tunnels

The layers #tracks-tunnels and #footbikecycle-tunnels are merged into #tunnels.
This is a preliminary step to merging the definitions for normal roads, tunnels, and bridges.

Consequences for rendering:
Rendering order of footways etc., paths and tracks is now determined by z_order instead of explicitly defining footways etc., paths and tracks to be rendered lowest.
Therefore, minor order changes between service roads, footways etc, paths, tracks in tunnels might occur.
Add missing key 'tracktype' to sql
Merge branch 'roadsv4.0' of https://github.com/math1985/openstreetmap-carto into math1985-roadsv4.0
Merge branch 'roadsv5a.0' of https://github.com/math1985/openstreetmap-carto into math1985-roadsv5a.0
Merge branch 'roadsv5a.1' of https://github.com/math1985/openstreetmap-carto into math1985-roadsv5a.1
Use 'layer in (...)' instead of repeated 'layer=...' in query.
Add the missing layer geometries.

Makes the little icons in the Tilemill layer menu show up properly.
Merge branch 'roadsv5b' of https://github.com/math1985/openstreetmap-carto into math1985-roadsv5b
Bump the dy on peaks, fixes https://trac.openstreetmap.org/ticket/4973
Remove commented style rule.
Add osm2pgsql style file to the repo.

The style file is inextricably linked with the style rules, much
more so than the version of osm2pgsql used. This allows us to add
or remove columns without requiring users to change their (perhaps
packaged) version of osm2pgsql.

Changes to this file usually requires reloading of databases, so
they will often be accompanied by major version increments.