Correct order secondary vs tertiary highway

This resolves #862.
Re-add highway=platform

Re-add highway=platform, and changes ordering of railway=platform versus paths.
This solves #871.

This assumes #866 is merged first.
Render ways with both highway and railway tag

Make sure that ways that have both a highway and a railway tag are rendered
both as highway and railway.

This resolves #874.

This assumes #866 and #884 are merged first.

Thanks to @kkofler.
Merge branch 'highway-railway-overlap' of https://github.com/math1985/openstreetmap-carto into math1985-highway-railway-overlap
Merge branch 'math1985-highway-railway-overlap'