Include tracktype, sac_scale, and more attributes on paths

[nvkelso]

See also:

• Show paths earlier: https://github.com/mapzen/vector-datasource/issues/593
• http://wiki.openstreetmap.org/wiki/Hiking

New properties:

• tracktype - grade1, grade2, grade3, grade4, grade5
• incline - value%, up, down
• trail_visibility - excellent, good, intermediate, bad, horrible, no
• sac_scale - hiking, mountain_hiking, demanding_mountain_hiking, alpine_hiking, demanding_alpine_hiking, difficult_alpine_hiking

[nvkelso]

• add new properties (on ways) to roads layer query
• build new tests after finding examples using TagInfo