A brighter hiking map

[zstadler]

A dark map is harder to see in the outdoors. Details and subtle lines tend to get unnoticed. See #199 for how dark the map looks compared to another map.

Potential improvements:

• Change the hillshade layer to use "hillshade-shadow-color": ["rgba(256,256,256,0)" rather than, or in addition to, "hillshade-highlight-color": ["rgba(256,256,256,0)"
• Add "line-opacity": 0.3 or lower to all contour layers.
• Use lightgray rather than gray for glacier outline.

Preliminary result:

Current:

[zstadler]

Follow-up tuning of the map could also consider changing the tone of road, as suggested in a #201