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
Round line caps for all roads

Make sure that all roads have a round line join.
No round line joins for bridges

Bridges should not have round line joins.
Merge branch 'master' of https://github.com/gravitystorm/openstreetmap-carto into casing
Remove rendering for highway=byway

Highway=byway should not render, as it has been deprecated for over three years.
Remove rendering for highway=unsurfaced

Highway=unsurfaced is not a highway type.
Update landcover.mss

changed commercial to construction to save gravitystorm's sanity:p
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.
Merge pull request #193 from wonderchook/master

Update landcover.mss
Change military hatching to 16px and use global alignment

Fixes #97
Change 'beirgarten' to 'biergarten' to fix a typo
Remove rendering of natural=bay areas

Fixes #164

Any natural=bay ways I checked were on top of water anyways.