✨ Sandwich layers under labels

[brianbancroft]

Sandwiches the new layers between the all of the basemap's point, polygon and polyline layers, and the basemaps' symbols, such as the labels.

https://www.useloom.com/share/aeef415e49c64766b5eeb83765db5d82

Warmup...

Not sure if we want this behaviour. Later on, this can be further enhanced through some boolean selector, that when toggled, removes all the custom PostGIS layers, and re-adds them in a manner which respects the preference.

TODO

• [x] Make this into a user-toggle
  • When toggled, the layer is removed and re-added in accordance with user preference

[chriswhong]

Added a toggle, even used moveLayer if the layer already exists on the map, so it doesn't flash!