Move leisure=track

[dch0ph]

Fixes #4726

Changes proposed in this pull request:

Move leisure=track and attraction=water_slide from amenity-line to landcover-line layer

[Also tweak to highway=ford SQL query to simplify hstore query]

Test rendering with links to the example places:

Before

Power line vs. track ordering

After

Unchanged renders for:

Ford as linear way

attraction=water_slide

Comments

As a ground-level feature, leisure=track is a very natural fit for early rendering in landcover-line. It's less obvious that water slides should be rendered e.g. before roller-coasters. Perhaps a future optimisation would be to merge many of these layers, so that the layer tag can be properly exploited?

[Note that #4104 proposes moving leisure=track to the roads layer (tricky) or aerialways and attraction=water_slide to waterway-bridges. It would make sense to consider these alternatives.]