Add option to turn off buildings and roads layers

[batpad]

Right now, when viewing Raster maps like the SOI maps, etc., the map is obstructed / overlayed by buildings and road layers that there is no current way to turn off.

I can see that there's situations where it's nice to see the context of present day roads and buildings, but I also think it's nice to be able to see the raster layers without overlays on top?

@planemad how hard would it be to make some sort of toggle for this? I think for now just a single toggle to "Show Roads and Buildings" or so, can be checked by default? It might be nice to have more granular control of layers to show, but I don't think we should worry about that right now?

@planemad does this seem reasonable and would you know how to implement this or where to look? I don't think I'd know quite where to start with the mapbox stuff.

[planemad]

👌 definitely an option we should have.

We can start with a general option: Basemap which just has an on/off toggle for the associated map layers.

Basic Implementation
map-layer-control.js

• Add support for a new layer type to map-layer-control.js for mapbox-streets. This type will not have any opacity control.
• On style.load read all the style layer ids with the tileset source mapbox://mapbox.mapbox-streets-v8 and store as an array for this layer control.
• When the layer control is toggled on/off, use https://docs.mapbox.com/mapbox-gl-js/example/toggle-layers/ to show/hide the associated list of layers

index.html

• Add a mapbox-streets layer to the MapLayerControl constructor

  title: 'Basemap',
  description: 'Buildings, Roads, Landuse and Place labels from [Mapbox Streets](https://docs.mapbox.com/data/tilesets/reference/mapbox-streets-v8/)',
  attribution: '[© Mapbox](https://www.mapbox.com/about/maps/), [© OpenStreetMap](https://www.openstreetmap.org/about/)'
  headerImage: 'assets/map-layer-mapbox.png',
  type: 'mapbox-streets',

In future, we can have sub layer control like 'Roads', Buildings', 'Places' each with a checkbox toggle or even style/color picker for finer customization.