Roads Refactor

[sensescape]

• update sphere map to improve terrain contrast
• adjust road colors (some cooler, some warming)
• remove special logic for "green area" roads in the mountain, mostly by...
• expand roads to double lines at most zooms
• adjust road stacking by zoom
• consolidate road labels to newer Tangram syntax (zoom stops)

[nvkelso]

This looks good and is ready to merge – but let's wait until after the current release is tagged.

[nvkelso]

Ready to merge (and master was tagged for v3.0.0)